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[Emacs-diffs] feature/tabs 3e0ad29: Frame-local tab-bar and window-local


From: Juri Linkov
Subject: [Emacs-diffs] feature/tabs 3e0ad29: Frame-local tab-bar and window-local tab-line.
Date: Sat, 31 Aug 2019 16:47:55 -0400 (EDT)

branch: feature/tabs
commit 3e0ad29a607c8c085de3b74c7505e417ad7f9062
Author: Juri Linkov <address@hidden>
Commit: Juri Linkov <address@hidden>

    Frame-local tab-bar and window-local tab-line.
    
    * etc/NEWS: Add 'tab-bar-mode' and 'global-tab-line-mode'.
    
    * etc/TODO: Remove tab-related items.
    
    * lisp/cus-start.el: Add tab-bar-mode, tab-bar-max-label-size.
    
    * lisp/frame.el (frame-notice-user-settings): handle tab-bar-lines.
    
    * lisp/loadup.el: Load "tab-bar".
    
    * lisp/menu-bar.el (menu-bar-options-save): Add tab-bar-mode.
    (menu-bar-showhide-menu): Define showhide-tab-bar.
    
    * lisp/startup.el (tab-bar-images-pixel-height): New defconst.
    (command-line): Reset tab-bar-mode.
    (x-apply-session-resources): Add "tabBar", "TabBar".
    
    * lisp/subr.el (read-key): Add tab-bar.
    
    * lisp/tab-bar.el: New file.
    * lisp/tab-line.el: New file.
    
    * lisp/window.el (window--dump-frame): Add tab-bar-height.
    
    * src/dispextern.h (enum window_part): Add ON_TAB_LINE.
    (struct glyph_matrix): Add tab_line_p.
    (struct glyph_row): Add tab_line_p.
    (MATRIX_TAB_LINE_ROW): New macro.
    (MATRIX_FIRST_TEXT_ROW): Handle more mode lines.
    (MR_PARTIALLY_VISIBLE_AT_TOP): Add WINDOW_TAB_LINE_HEIGHT.
    (MATRIX_TAB_LINE_HEIGHT, CURRENT_TAB_LINE_HEIGHT)
    (DESIRED_TAB_LINE_HEIGHT): New macros.
    (enum face_id): Add TAB_BAR_FACE_ID and TAB_LINE_FACE_ID.
    (struct it): Add tab_line_p.
    (tab_bar_item_idx, tab_bar_item_image): New enums.
    (DEFAULT_TAB_BAR_LABEL_SIZE, DEFAULT_TAB_BAR_BUTTON_MARGIN)
    (DEFAULT_TAB_BAR_BUTTON_RELIEF, DEFAULT_TAB_BAR_IMAGE_HEIGHT):
    New constants.
    
    * src/dispnew.c (adjust_glyph_matrix): Use window_wants_tab_line.
    (shift_glyph_matrix): Add WINDOW_TAB_LINE_HEIGHT.
    (clear_current_matrices, clear_desired_matrices):
    Call clear_glyph_matrix on tab_bar_window.
    (blank_row): Add WINDOW_TAB_LINE_HEIGHT.
    (required_matrix_height): Change 2 to 3.
    (fake_current_matrices): Reset tab_line_p.
    (adjust_frame_glyphs_for_window_redisplay): Handle tab_bar_window.
    Add FRAME_TAB_BAR_HEIGHT and FRAME_TAB_BAR_LINES.
    (free_glyphs): Handle tab_bar_window.
    (update_frame): Handle tab_bar_window.
    (update_window): Handle row->tab_line_p.
    (scrolling_window): Change arg type from bool to int.
    Change header_line_p to tab_line_p.
    (buffer_posn_from_coords): Add window_wants_tab_line.
    (mode_line_string): Use MATRIX_TAB_LINE_ROW for part ON_TAB_LINE.
    
    * src/frame.c (frame_default_tab_bar_height): New internal variable.
    (adjust_frame_size): Handle tab_bar_window.
    (make_frame): Reset tab_bar_redisplayed, tab_bar_resized and
    last_tab_bar_item.
    (Ftab_bar_pixel_width): New function.
    (frame_parms): Add tab-bar-lines.
    (gui_figure_window_size): Add new arg tabbar_p.
    (syms_of_frame): Add Qtab_bar_size, Qupdate_frame_tab_bar,
    Qfree_frame_tab_bar, Qtab_bar_lines, Stab_bar_pixel_width.
    Add Qtab_bar_lines to frame_inhibit_implied_resize.
    (tab-bar-mode): New variable.
    
    * src/frame.h (GCALIGNED_STRUCT): Add tab_bar_window,
    desired_tab_bar_string, current_tab_bar_string.
    (GCALIGNED_STRUCT): Add tab_bar_items, last_tab_bar_item,
    minimize_tab_bar_window_p, tab_bar_redisplayed, tab_bar_resized,
    tab_bar_lines, tab_bar_height, n_tab_bar_rows, n_tab_bar_items.
    (fset_tab_bar_items, fset_tab_bar_window)
    (fset_current_tab_bar_string, fset_desired_tab_bar_string):
    New inlines.
    (FRAME_TAB_BAR_LINES, FRAME_TAB_BAR_HEIGHT): New macros.
    (FRAME_TOP_MARGIN, FRAME_TOP_MARGIN_HEIGHT):
    Use FRAME_TAB_BAR_LINES.
    
    * src/fringe.c (draw_fringe_bitmap_1, update_window_fringes):
    Add WINDOW_TAB_LINE_HEIGHT.
    
    * src/gtkutil.c (xg_frame_set_char_size): Add FRAME_TABBAR_WIDTH.
    (x_wm_set_size_hint): Add FRAME_TABBAR_WIDTH.
    
    * src/keyboard.c (read_char): Handle Qtab_bar.
    (kbd_buffer_get_event): Handle TAB_BAR_EVENT.
    (make_lispy_position): Add WINDOW_TAB_LINE_HEIGHT.
    Handle TAB_BAR_EVENT.
    (tab_bar_items_vector, tab_bar_item_properties, ntab_bar_items):
    New internal variables.
    (tab_bar_items, process_tab_bar_item, set_prop_tab_bar)
    (parse_tab_bar_item, init_tab_bar_items, append_tab_bar_item):
    New functions.
    (read_char_x_menu_prompt, read_key_sequence): Handle Qtab_bar.
    (tab-bar-separator-image-expression): New variable.
    
    * src/keymap.c (syms_of_keymap): Add Qtab_bar and Qtab_line.
    
    * src/menu.c (x_popup_menu_1, Fx_popup_dialog): Handle Qtab_bar.
    
    * src/termhooks.h (enum event_kind): Add TAB_BAR_EVENT.
    (GCALIGNED_STRUCT): Add change_tab_bar_height_hook.
    
    * src/w32fns.c (w32_frame_parm_handlers): Add w32_set_tab_bar_lines.
    
    * src/w32term.c (w32_draw_window_cursor): Add WINDOW_TAB_LINE_HEIGHT.
    
    * src/window.c (window_body_height): Add WINDOW_TAB_LINE_HEIGHT.
    (Fwindow_tab_line_height): New function.
    (coordinates_in_window): Use window_wants_tab_line with
    CURRENT_TAB_LINE_HEIGHT.
    (window_relative_x_coord): Add ON_TAB_LINE.
    (Fcoordinates_in_window_p): Add ON_TAB_LINE.
    (window_from_coordinates): Add new arg tab_bar_p.
    (Fwindow_line_height): Use window_wants_tab_line with
    WINDOW_TAB_LINE_HEIGHT.
    (Fwindow_lines_pixel_dimensions): Add WINDOW_TAB_LINE_HEIGHT.
    (make_window): Set tab_line_height to -1.
    (window_wants_tab_line): New function.
    (window_internal_height): Use window_wants_tab_line.
    (window_scroll_pixel_based): Add WINDOW_TAB_LINE_HEIGHT.
    (Frecenter): Set minimize_tab_bar_window_p to 1.
    (GCALIGNED_STRUCT): Add frame_tab_bar_lines and frame_tab_bar_height.
    (Fcurrent_window_configuration): Set frame_tab_bar_lines and
    frame_tab_bar_height.
    (set_window_scroll_bars): Add WINDOW_TAB_LINE_HEIGHT.
    (syms_of_window): Add Qtab_line_format and Swindow_tab_line_height.
    
    * src/window.h (GCALIGNED_STRUCT): Add tab_line_height.
    (WINDOW_TAB_BAR_P, WINDOW_TAB_LINE_HEIGHT, WINDOW_TAB_LINE_LINES):
    New macros.
    (WINDOW_TOP_EDGE_Y, WINDOW_BOTTOM_EDGE_Y, WINDOW_TAB_LINE_HEIGHT):
    Add WINDOW_TAB_BAR_P.
    
    * src/xdisp.c (window_box_height): Add window_wants_tab_line with
    MATRIX_TAB_LINE_ROW and CURRENT_TAB_LINE_HEIGHT.
    (pos_visible_p): Use window_wants_tab_line.
    Add WINDOW_TAB_LINE_HEIGHT.
    (get_glyph_string_clip_rects): Add WINDOW_TAB_LINE_HEIGHT.
    (get_phys_cursor_geometry): Add WINDOW_TAB_LINE_HEIGHT.
    (remember_mouse_glyph): Use MATRIX_TAB_LINE_ROW for part
    ON_TAB_LINE.
    (init_iterator): Use MATRIX_TAB_LINE_ROW for TAB_LINE_FACE_ID.
    Add WINDOW_TAB_LINE_HEIGHT.  Add window_wants_tab_line.
    (Fwindow_text_pixel_size): Add WINDOW_TAB_LINE_HEIGHT.
    (prepare_menu_bars): Call update_tab_bar.
    (update_tab_bar, build_desired_tab_bar_string)
    (display_tab_bar_line, tab_bar_height, Ftab_bar_height)
    (redisplay_tab_bar, tab_bar_item_info, get_tab_bar_item)
    (handle_tab_bar_click, note_tab_bar_highlight): New functions.
    (compute_window_start_on_continuation_line): Use window_wants_tab_line.
    (try_cursor_movement): Use window_wants_tab_line with
    CURRENT_TAB_LINE_HEIGHT.
    (redisplay_window): Use window_wants_tab_line with
    CURRENT_TAB_LINE_HEIGHT.
    (try_window_reusing_current_matrix): Use window_wants_tab_line
    with WINDOW_TAB_LINE_HEIGHT.
    (Fdump_tab_bar_row): New function.
    (compute_line_metrics): Add WINDOW_TAB_LINE_HEIGHT.
    (display_line): Use window_wants_tab_line.
    (display_mode_line): Set tab_line_p to true if face_id is
    TAB_LINE_FACE_ID.
    (Fformat_mode_line): Handle Qtab_line and Qtab_bar.
    (gui_clear_end_of_line): Add WINDOW_TAB_LINE_HEIGHT.
    (erase_phys_cursor): Use WINDOW_TAB_LINE_HEIGHT.
    (show_mouse_face): Use tab_bar_window.
    (note_mode_line_or_margin_highlight): Use MATRIX_TAB_LINE_ROW for
    area ON_TAB_LINE.
    (note_mouse_highlight): Call note_tab_bar_highlight,
    (expose_frame): Handle tab_bar_window.
    (syms_of_xdisp): Add Sdump_tab_bar_row and Stab_bar_height.
    (auto-resize-tab-bars, auto-raise-tab-bar-buttons)
    (tab-bar-border, tab-bar-button-margin, tab-bar-button-relief)
    (tab-bar-max-label-size): New variables.
    
    * src/xfaces.c (lookup_basic_face): Add TAB_LINE_FACE_ID and
    TAB_BAR_FACE_ID.
    (syms_of_xfaces): Define Qtab_bar and Qtab_line.
    
    * src/xfns.c (x_set_tab_bar_lines, x_change_tab_bar_height):
    New functions.
    (xic_set_statusarea): Add FRAME_TABBAR_TOP_HEIGHT.
    (frame_geometry): Add FRAME_TAB_BAR_HEIGHT and Qtab_bar_size.
    
    * src/xterm.c (x_draw_image_relief): Use tab_bar_button_relief.
    (x_draw_image_relief): Use TAB_BAR_FACE_ID.
    (handle_one_xevent): Handle tab_bar_window.
    (x_set_window_size_1): Add FRAME_TABBAR_WIDTH.
    (x_create_terminal): Set change_tab_bar_height_hook.
    
    * src/xterm.h (struct x_output): Add tabbar_top_height,
    tabbar_bottom_height, tabbar_left_width, tabbar_right_width
    tabbar_widget, tabbar_in_hbox, tabbar_is_packed.
    (FRAME_TABBAR_TOP_HEIGHT): Add FRAME_TABBAR_TOP_HEIGHT,
    FRAME_TABBAR_BOTTOM_HEIGHT, FRAME_TABBAR_HEIGHT,
    FRAME_TABBAR_LEFT_WIDTH, FRAME_TABBAR_RIGHT_WIDTH,
    FRAME_TABBAR_WIDTH.
---
 etc/NEWS          |   17 +
 etc/TODO          |   14 -
 lisp/cus-start.el |    6 +
 lisp/frame.el     |   42 ++
 lisp/loadup.el    |    3 +-
 lisp/menu-bar.el  |   11 +-
 lisp/startup.el   |    5 +
 lisp/subr.el      |    6 +-
 lisp/tab-bar.el   |  395 +++++++++++++++++
 lisp/tab-line.el  |  264 ++++++++++++
 lisp/window.el    |    5 +-
 src/buffer.c      |    2 +-
 src/dispextern.h  |  136 +++++-
 src/dispnew.c     |  152 ++++++-
 src/frame.c       |   82 +++-
 src/frame.h       |   72 +++-
 src/fringe.c      |    8 +-
 src/gtkutil.c     |    8 +-
 src/keyboard.c    |  505 +++++++++++++++++++++-
 src/keymap.c      |    2 +-
 src/lisp.h        |    1 +
 src/menu.c        |    2 +
 src/msdos.c       |    2 +-
 src/termhooks.h   |    8 +
 src/w32fns.c      |    5 +-
 src/w32inevt.c    |    2 +-
 src/w32term.c     |    6 +-
 src/window.c      |  123 +++++-
 src/window.h      |   36 +-
 src/xdisp.c       | 1223 ++++++++++++++++++++++++++++++++++++++++++++++-------
 src/xfaces.c      |    6 +
 src/xfns.c        |  108 ++++-
 src/xterm.c       |   57 ++-
 src/xterm.h       |   25 ++
 34 files changed, 3073 insertions(+), 266 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 9a3725b..fe49f8f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1883,6 +1883,23 @@ good replacement, even in very large source files.
 
 * New Modes and Packages in Emacs 27.1
 
+** 'tab-bar-mode' enables the tab-bar at the top of each frame,
+to switch named persistent window configurations in it using tabs.
+New tab-based keybindings (similar to frame-based):
+'C-x 6 2' creates a new tab;
+'C-x 6 b' switches to buffer in another tab;
+'C-x 6 f' and 'C-x 6 C-f' edit file in another tab;
+'C-TAB' switches to the next tab;
+'S-C-TAB' switches to the previous tab.
+
+** 'global-tab-line-mode' enables the tab-line above each window to
+switch buffers in it to previous/next buffers.  Selecting a previous
+window-local tab is the same as running 'C-x <left>' (previous-buffer),
+selecting a next tab switches to the tab available by 'C-x <right>'
+(next-buffer).  Clicking on the plus icon adds a new buffer to the
+window-local tab-line of window buffers.  Using the mouse wheel on the
+tab-line scrolls the window buffers whose names are displayed in tabs.
+
 ** fileloop.el lets one setup multifile operations like search&replace.
 
 +++
diff --git a/etc/TODO b/etc/TODO
index a065763..ce76ccf 100644
--- a/etc/TODO
+++ b/etc/TODO
@@ -276,20 +276,6 @@ consistency checks that make sure the new code computes 
the same results
 as the old code.  And once that works well, we can remove the old code
 and old fields.
 
-** Having tabs above a window to switch buffers in it.
-
-** "Perspectives" are named persistent window configurations.  We have
-had the window configuration mechanism in GNU Emacs since the
-beginning but we have never developed a good user interface to take
-advantage of them.  Eclipse's user interface seems to be good.
-
-Perspectives work well even if you do the equivalent of C-x 4 C-f
-because of the distinction between view windows vs file windows.  In
-Emacs this is more or less the "dedicated window" feature, but we have
-never really made it work for this.
-
-Perspectives also need to interact with the tabs.
-
 ** FFI (foreign function interface)
 See eg https://lists.gnu.org/r/emacs-devel/2013-10/msg00246.html
 
diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index 15d33b43..d5d5c6a 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -324,6 +324,9 @@ Leaving \"Default\" unchecked is equivalent with specifying 
a default of
                            ;; FIXME?
                             ;; :initialize custom-initialize-default
                            :set custom-set-minor-mode)
+            (tab-bar-mode (frames mouse) boolean nil
+                           ;; :initialize custom-initialize-default
+                          :set custom-set-minor-mode)
             (tool-bar-mode (frames mouse) boolean nil
                             ;; :initialize custom-initialize-default
                            :set custom-set-minor-mode)
@@ -588,6 +591,7 @@ since it could result in memory overflow and make Emacs 
crash."
                      (const :tag "Text-image-horiz" :value text-image-horiz)
                      (const :tag "System default" :value nil)) "24.1")
              (tool-bar-max-label-size frames integer "24.1")
+             (tab-bar-max-label-size frames integer "27.1")
             (auto-hscroll-mode scrolling
                                 (choice
                                  (const :tag "Don't scroll automatically"
@@ -726,6 +730,8 @@ since it could result in memory overflow and make Emacs 
crash."
                      ;; the condition for loadup.el to preload tool-bar.el.
                      ((string-match "tool-bar-" (symbol-name symbol))
                       (fboundp 'x-create-frame))
+                     ((string-match "tab-bar-" (symbol-name symbol))
+                      (fboundp 'x-create-frame))
                      ((equal "vertical-centering-font-regexp"
                              (symbol-name symbol))
                       ;; Any function from fontset.c will do.
diff --git a/lisp/frame.el b/lisp/frame.el
index fd7e872..374c92f 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -363,6 +363,47 @@ there (in decreasing order of priority)."
     ;; If the initial frame is still around, apply initial-frame-alist
     ;; and default-frame-alist to it.
     (when (frame-live-p frame-initial-frame)
+      ;; When tab-bar has been switched off, correct the frame size
+      ;; by the lines added in x-create-frame for the tab-bar and
+      ;; switch `tab-bar-mode' off.
+      (when (display-graphic-p)
+       (let* ((init-lines
+               (assq 'tab-bar-lines initial-frame-alist))
+              (other-lines
+               (or (assq 'tab-bar-lines window-system-frame-alist)
+                   (assq 'tab-bar-lines default-frame-alist)))
+              (lines (or init-lines other-lines))
+              (height (tab-bar-height frame-initial-frame t)))
+         ;; Adjust frame top if either zero (nil) tab bar lines have
+         ;; been requested in the most relevant of the frame's alists
+         ;; or tab bar mode has been explicitly turned off in the
+         ;; user's init file.
+         (when (and (> height 0)
+                    (or (and lines
+                             (or (null (cdr lines))
+                                 (eq 0 (cdr lines))))
+                        (not tab-bar-mode)))
+           (let* ((initial-top
+                   (cdr (assq 'top frame-initial-geometry-arguments)))
+                  (top (frame-parameter frame-initial-frame 'top)))
+             (when (and (consp initial-top) (eq '- (car initial-top)))
+               (let ((adjusted-top
+                      (cond
+                       ((and (consp top) (eq '+ (car top)))
+                        (list '+ (+ (cadr top) height)))
+                       ((and (consp top) (eq '- (car top)))
+                        (list '- (- (cadr top) height)))
+                       (t (+ top height)))))
+                 (modify-frame-parameters
+                  frame-initial-frame `((top . ,adjusted-top))))))
+           ;; Reset `tab-bar-mode' when zero tab bar lines have been
+           ;; requested for the window-system or default frame alists.
+           (when (and tab-bar-mode
+                      (and other-lines
+                           (or (null (cdr other-lines))
+                               (eq 0 (cdr other-lines)))))
+             (tab-bar-mode -1)))))
+
       ;; When tool-bar has been switched off, correct the frame size
       ;; by the lines added in x-create-frame for the tool-bar and
       ;; switch `tool-bar-mode' off.
@@ -1593,6 +1634,7 @@ and width values are in pixels.
        '(tool-bar-external . nil)
        '(tool-bar-position . nil)
        '(tool-bar-size 0 . 0)
+       '(tab-bar-size 0 . 0)
        (cons 'internal-border-width
             (frame-parameter frame 'internal-border-width)))))))
 
diff --git a/lisp/loadup.el b/lisp/loadup.el
index 67e8aa7..9360cd4 100644
--- a/lisp/loadup.el
+++ b/lisp/loadup.el
@@ -290,7 +290,8 @@
       (load "image")
       (load "international/fontset")
       (load "dnd")
-      (load "tool-bar")))
+      (load "tool-bar")
+      (load "tab-bar")))
 
 (if (featurep 'dynamic-setting)
     (load "dynamic-setting"))
diff --git a/lisp/menu-bar.el b/lisp/menu-bar.el
index 389234e..112b567 100644
--- a/lisp/menu-bar.el
+++ b/lisp/menu-bar.el
@@ -687,7 +687,7 @@ The selected font will be the default on both the existing 
and future frames."
                   ;; side-effect that turning them off via X
                   ;; resources acts like having customized them, but
                   ;; that seems harmless.
-                  menu-bar-mode tool-bar-mode))
+                  menu-bar-mode tab-bar-mode tool-bar-mode))
       ;; FIXME ? It's a little annoying that running this command
       ;; always loads cua-base, paren, time, and battery, even if they
       ;; have not been customized in any way.  (Due to custom-load-symbol.)
@@ -1242,6 +1242,15 @@ mail status in mode line"))
                               (frame-parameter (menu-bar-frame-for-menubar)
                                                'menu-bar-lines)))))
 
+    (bindings--define-key menu [showhide-tab-bar]
+      '(menu-item "Tab Bar" toggle-tab-bar-mode-from-frame
+                  :help "Turn tab bar on/off"
+                  :visible (display-graphic-p)
+                  :button
+                  (:toggle . (menu-bar-positive-p
+                              (frame-parameter (menu-bar-frame-for-menubar)
+                                               'tab-bar-lines)))))
+
     (if (and (boundp 'menu-bar-showhide-tool-bar-menu)
              (keymapp menu-bar-showhide-tool-bar-menu))
         (bindings--define-key menu [showhide-tool-bar]
diff --git a/lisp/startup.el b/lisp/startup.el
index c1e429b..2ab4a3a 100644
--- a/lisp/startup.el
+++ b/lisp/startup.el
@@ -731,6 +731,9 @@ It is the default value of the variable `top-level'."
     ("--background-color" . "-bg")
     ("--color"           . "-color")))
 
+(defconst tab-bar-images-pixel-height 18
+  "Height in pixels of images in the tab-bar.")
+
 (defconst tool-bar-images-pixel-height 24
   "Height in pixels of images in the tool-bar.")
 
@@ -1264,6 +1267,7 @@ please check its value")
   (unless (daemonp)
     (if (or noninteractive emacs-basic-display)
        (setq menu-bar-mode nil
+             tab-bar-mode nil
              tool-bar-mode nil
              no-blinking-cursor t))
     (frame-initialize))
@@ -1479,6 +1483,7 @@ This can set the values of `menu-bar-mode', 
`tool-bar-mode', and
 settings will be marked as \"CHANGED outside of Customize\"."
   (let ((no-vals  '("no" "off" "false" "0"))
        (settings '(("menuBar" "MenuBar" menu-bar-mode nil)
+                   ("tabBar" "TabBar" tab-bar-mode nil)
                    ("toolBar" "ToolBar" tool-bar-mode nil)
                    ("scrollBar" "ScrollBar" scroll-bar-mode nil)
                    ("cursorBlink" "CursorBlink" no-blinking-cursor t))))
diff --git a/lisp/subr.el b/lisp/subr.el
index 566a3fc..6aa5a09 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2395,8 +2395,12 @@ some sort of escape sequence, the ambiguity is resolved 
via `read-key-delay'."
         (progn
          (use-global-map
            (let ((map (make-sparse-keymap)))
-             ;; Don't hide the menu-bar and tool-bar entries.
+             ;; Don't hide the menu-bar, tab-bar and tool-bar entries.
              (define-key map [menu-bar] (lookup-key global-map [menu-bar]))
+             (define-key map [tab-bar]
+              ;; This hack avoids evaluating the :filter (Bug#9922).
+              (or (cdr (assq 'tab-bar global-map))
+                  (lookup-key global-map [tab-bar])))
              (define-key map [tool-bar]
               ;; This hack avoids evaluating the :filter (Bug#9922).
               (or (cdr (assq 'tool-bar global-map))
diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
new file mode 100644
index 0000000..a522418
--- /dev/null
+++ b/lisp/tab-bar.el
@@ -0,0 +1,395 @@
+;;; tab-bar.el --- frame-local tab bar with window configurations -*- 
lexical-binding: t; -*-
+
+;; Copyright (C) 2019 Free Software Foundation, Inc.
+
+;; Author: Juri Linkov <address@hidden>
+;; Keywords: frames tabs
+;; Maintainer: address@hidden
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Provides `tab-bar-mode' to control display of the tab-bar and
+;; bindings for the global tab bar.
+
+;; The normal global binding for [tab-bar] (below) uses the value of
+;; `tab-bar-map' as the actual keymap to define the tab bar.  Modes
+;; may either bind items under the [tab-bar] prefix key of the local
+;; map to add to the global bar or may set `tab-bar-map'
+;; buffer-locally to override it.
+
+;;; Code:
+
+
+(defgroup tab-bar nil
+  "Frame-local tab bar."
+  :group 'convenience
+  :version "27.1")
+
+(defgroup tab-bar-faces nil
+  "Faces used in the tab bar."
+  :group 'tab-bar
+  :group 'faces
+  :version "27.1")
+
+(defface tab-bar
+  '((default
+     :box (:line-width 1 :style released-button)
+     :foreground "black")
+    (((type x w32 ns) (class color))
+     :background "grey75")
+    (((type x) (class mono))
+     :background "grey"))
+  "Tab bar face."
+  :version "27.1"
+  :group 'tab-bar-faces)
+
+(defface tab-bar-tab
+  '((default
+      :inherit tab-bar-tab-inactive)
+    (t
+     :background "grey75"))
+  "Tab bar face for selected tab."
+  :version "27.1"
+  :group 'tab-bar-faces)
+
+(defface tab-bar-tab-inactive
+  '((((class color) (min-colors 88))
+     :box (:line-width -15 :style pressed-button)
+     :background "grey60")
+    (t
+     :inherit highlight))
+  "Tab bar face for non-selected tab."
+  :version "27.1"
+  :group 'tab-bar-faces)
+
+
+(define-minor-mode tab-bar-mode
+  "Toggle the tab bar in all graphical frames (Tab Bar mode)."
+  :global t
+  ;; It's defined in C/cus-start, this stops the d-m-m macro defining it again.
+  :variable tab-bar-mode
+  (let ((val (if tab-bar-mode 1 0)))
+    (dolist (frame (frame-list))
+      (set-frame-parameter frame 'tab-bar-lines val))
+    ;; If the user has given `default-frame-alist' a `tab-bar-lines'
+    ;; parameter, replace it.
+    (if (assq 'tab-bar-lines default-frame-alist)
+        (setq default-frame-alist
+              (cons (cons 'tab-bar-lines val)
+                    (assq-delete-all 'tab-bar-lines
+                                     default-frame-alist)))))
+  (when tab-bar-mode
+    (global-set-key [(control shift iso-lefttab)] 'tab-bar-switch-to-prev-tab)
+    (global-set-key [(control tab)]               
'tab-bar-switch-to-next-tab)))
+
+;;;###autoload
+;; Used in the Show/Hide menu, to have the toggle reflect the current frame.
+(defun toggle-tab-bar-mode-from-frame (&optional arg)
+  "Toggle tab bar on or off, based on the status of the current frame.
+See `tab-bar-mode' for more information."
+  (interactive (list (or current-prefix-arg 'toggle)))
+  (if (eq arg 'toggle)
+      (tab-bar-mode (if (> (frame-parameter nil 'tab-bar-lines) 0) 0 1))
+    (tab-bar-mode arg)))
+
+(defvar tab-bar-map (make-sparse-keymap)
+  "Keymap for the tab bar.
+Define this locally to override the global tab bar.")
+
+(global-set-key [tab-bar]
+                `(menu-item ,(purecopy "tab bar") ignore
+                            :filter tab-bar-make-keymap))
+
+(defconst tab-bar-keymap-cache (make-hash-table :weakness t :test 'equal))
+
+(defun tab-bar-make-keymap (&optional _ignore)
+  "Generate an actual keymap from `tab-bar-map'.
+Its main job is to show tabs in the tab bar."
+  (if (= 1 (length tab-bar-map))
+      (tab-bar-make-keymap-1)
+    (let ((key (cons (frame-terminal) tab-bar-map)))
+      (or (gethash key tab-bar-keymap-cache)
+          (puthash key tab-bar-map tab-bar-keymap-cache)))))
+
+
+(defvar tab-bar-separator " ")
+(defvar tab-bar-tab-name-add nil)
+(defvar tab-bar-tab-name-close nil)
+
+(defun tab-bar-tab-name ()
+  "Generate tab name in the context of the selected frame."
+  (mapconcat
+   (lambda (w) (buffer-name (window-buffer w)))
+   (window-list)
+   ", "))
+
+(defun tab-bar-tabs ()
+  "Return a list of tabs belonging to the selected frame.
+Ensure the frame parameter `tabs' is pre-populated.
+Return its existing value or a new value."
+  (let ((tabs (frame-parameter nil 'tabs)))
+    (unless tabs
+      (setq tabs `((current-tab (name . ,(tab-bar-tab-name)))))
+      (set-frame-parameter nil 'tabs tabs))
+    tabs))
+
+(defun tab-bar-make-keymap-1 ()
+  "Generate an actual keymap from `tab-bar-map', without caching."
+  (let ((i 0))
+    (append
+     '(keymap)
+     (mapcan
+      (lambda (tab)
+        (setq i (1+ i))
+        (list (cond
+               ((eq (car tab) 'current-tab)
+                `(current-tab
+                  menu-item
+                  ,(propertize "Current tab" 'face 'tab-bar-tab)
+                  ignore
+                  :help "Current tab"))
+               (t
+                `(,(intern (format "tab-%i" i))
+                  menu-item
+                  ,(propertize (cdr (assq 'name tab)) 'face 
'tab-bar-tab-inactive)
+                  ,(lambda ()
+                     (interactive)
+                     (tab-bar-select-tab tab))
+                  :help "Click to visit tab")))
+              `(,(intern (format "close-tab-%i" i))
+                menu-item
+                ,(concat (propertize (or tab-bar-tab-name-close
+                                         (if (char-displayable-p ?⮿) "⮿" 
"[x]"))
+                                     'face (if (eq (car tab) 'current-tab)
+                                               'tab-bar-tab
+                                             'tab-bar-tab-inactive))
+                         tab-bar-separator)
+                ,(lambda ()
+                   (interactive)
+                   (tab-bar-close-tab tab))
+                :help "Click to close tab")))
+      (tab-bar-tabs))
+     `((add-tab menu-item
+                ,(propertize (or tab-bar-tab-name-add
+                                 (if (char-displayable-p ?➕) "➕" "[+]"))
+                             'face 'tab-bar-tab-inactive)
+                tab-bar-add-tab
+                :help "Click to add tab")))))
+
+
+(defun tab-bar-read-tab-name (prompt)
+  (let* ((tabs (tab-bar-tabs))
+         (tab-name
+          (completing-read prompt
+                           (or (delq nil (mapcar (lambda (tab)
+                                                   (cdr (assq 'name tab)))
+                                                 tabs))
+                               '("")))))
+    (catch 'done
+      (dolist (tab tabs)
+        (when (equal (cdr (assq 'name tab)) tab-name)
+          (throw 'done tab))))))
+
+(defun tab-bar-new-tab ()
+  (let ((tab `(tab
+               (name . ,(tab-bar-tab-name))
+               (wc . ,(current-window-configuration))
+               (ws . ,(window-state-get
+                       (frame-root-window (selected-frame)) 'writable)))))
+    tab))
+
+(defun tab-bar-find-prev-tab (&optional tabs)
+  (unless tabs
+    (setq tabs (tab-bar-tabs)))
+  (unless (eq (car (car tabs)) 'current-tab)
+    (while (and tabs (not (eq (car (car (cdr tabs))) 'current-tab)))
+      (setq tabs (cdr tabs)))
+    tabs))
+
+
+(defun tab-bar-select-tab (tab)
+  "Switch to the specified TAB."
+  (interactive (list (tab-bar-read-tab-name "Select tab by name: ")))
+  (when (and tab (not (eq (car tab) 'current-tab)))
+    (let* ((tabs (tab-bar-tabs))
+           (new-tab (tab-bar-new-tab))
+           (wc (cdr (assq 'wc tab))))
+      ;; During the same session, use window-configuration to switch
+      ;; tabs, because window-configurations are more reliable
+      ;; (they keep references to live buffers) than window-states.
+      ;; But after restoring tabs from a previously saved session,
+      ;; its value of window-configuration is unreadable,
+      ;; so restore its saved window-state.
+      (if (window-configuration-p wc)
+          (set-window-configuration wc)
+        (window-state-put (cdr (assq 'ws tab))
+                          (frame-root-window (selected-frame)) 'safe))
+      (while tabs
+        (cond
+         ((eq (car tabs) tab)
+          (setcar tabs `(current-tab (name . ,(tab-bar-tab-name)))))
+         ((eq (car (car tabs)) 'current-tab)
+          (setcar tabs new-tab)))
+        (setq tabs (cdr tabs)))
+      (force-window-update))))
+
+(defun tab-bar-switch-to-prev-tab ()
+  "Switch to the previous tab."
+  (interactive)
+  (let ((prev-tab (tab-bar-find-prev-tab)))
+    (when prev-tab
+      (tab-bar-select-tab (car prev-tab)))))
+
+(defun tab-bar-switch-to-next-tab ()
+  "Switch to the next tab."
+  (interactive)
+  (let* ((tabs (tab-bar-tabs))
+         (prev-tab (tab-bar-find-prev-tab tabs)))
+    (if prev-tab
+        (tab-bar-select-tab (car (cdr (cdr prev-tab))))
+      (tab-bar-select-tab (car (cdr tabs))))))
+
+
+(defcustom tab-bar-add-tab-to 'right
+  "Defines where to create a new tab.
+If `leftmost', create as the first tab.
+If `left', create to the left from the current tab.
+If `right', create to the right from the current tab.
+If `rightmost', create as the last tab."
+  :type '(choice (const :tag "First tab" leftmost)
+                 (const :tag "To the left" left)
+                 (const :tag "To the right" right)
+                 (const :tag "Last tab" rightmost))
+  :version "27.1")
+
+(defun tab-bar-add-tab ()
+  "Clone the current tab to the position specified by `tab-bar-add-tab-to'."
+  (interactive)
+  (unless tab-bar-mode
+    (tab-bar-mode 1))
+  (let* ((tabs (tab-bar-tabs))
+         ;; (i-tab (- (length tabs) (length (memq tab tabs))))
+         (new-tab (tab-bar-new-tab)))
+    (cond
+     ((eq tab-bar-add-tab-to 'leftmost)
+      (setq tabs (cons new-tab tabs)))
+     ((eq tab-bar-add-tab-to 'rightmost)
+      (setq tabs (append tabs (list new-tab))))
+     (t
+      (let ((prev-tab (tab-bar-find-prev-tab tabs)))
+        (cond
+         ((eq tab-bar-add-tab-to 'left)
+          (if prev-tab
+              (setcdr prev-tab (cons new-tab (cdr prev-tab)))
+            (setq tabs (cons new-tab tabs))))
+         ((eq tab-bar-add-tab-to 'right)
+          (if prev-tab
+              (setq prev-tab (cdr prev-tab))
+            (setq prev-tab tabs))
+          (setcdr prev-tab (cons new-tab (cdr prev-tab))))))))
+    (set-frame-parameter nil 'tabs tabs)
+    (tab-bar-select-tab new-tab)))
+
+
+(defcustom tab-bar-close-tab-select 'right
+  "Defines what tab to select after closing the specified tab.
+If `left', select the adjacent left tab.
+If `right', select the adjacent right tab."
+  :type '(choice (const :tag "Select left tab" left)
+                 (const :tag "Select right tab" right))
+  :version "27.1")
+
+(defun tab-bar-close-current-tab (tab)
+  "Close the current TAB.
+After closing the current tab switch to the tab
+specified by `tab-bar-close-tab-select'."
+  (interactive
+   (list
+    (let* ((tabs (tab-bar-tabs))
+           (prev-tab (tab-bar-find-prev-tab tabs)))
+      (if prev-tab
+          (tab-bar-select-tab (car prev-tab))
+        (car tabs)))))
+  (let* ((tabs (tab-bar-tabs))
+         (i-tab (- (length tabs) (length (memq tab tabs))))
+         (i-select
+          (cond
+           ((eq tab-bar-close-tab-select 'left)
+            (1- i-tab))
+           ((eq tab-bar-close-tab-select 'right)
+            ;; Do nothing: the next tab will take
+            ;; the index of the closed tab
+            i-tab)
+           (t 0)))
+         (tabs (delq tab tabs))
+         (i-select (max 0 (min (1- (length tabs)) i-select)))
+         (select-tab (nth i-select tabs)))
+    (set-frame-parameter nil 'tabs tabs)
+    (tab-bar-select-tab select-tab)))
+
+(defun tab-bar-close-tab (tab)
+  "Close the specified TAB.
+After closing the current tab switch to the tab
+specified by `tab-bar-close-tab-select'."
+  (interactive (list (tab-bar-read-tab-name "Close tab by name: ")))
+  (when tab
+    (if (eq (car tab) 'current-tab)
+        (tab-bar-close-current-tab tab)
+      ;; Close non-current tab, no need to switch to another tab
+      (set-frame-parameter nil 'tabs (delq tab (tab-bar-tabs)))
+      (force-window-update))))
+
+
+(defvar ctl-x-6-map (make-sparse-keymap)
+  "Keymap for tab commands.")
+(defalias 'ctl-x-6-prefix ctl-x-6-map)
+(define-key ctl-x-map "6" 'ctl-x-6-prefix)
+
+(defun switch-to-buffer-other-tab (buffer-or-name &optional norecord)
+  "Switch to buffer BUFFER-OR-NAME in another tab.
+Like \\[switch-to-buffer-other-frame] (which see), but creates a new tab."
+  (interactive
+   (list (read-buffer-to-switch "Switch to buffer in other tab: ")))
+  (tab-bar-add-tab)
+  (delete-other-windows)
+  (switch-to-buffer buffer-or-name norecord))
+
+(defun find-file-other-tab (filename &optional wildcards)
+  "Edit file FILENAME, in another tab.
+Like \\[find-file-other-frame] (which see), but creates a new tab."
+  (interactive
+   (find-file-read-args "Find file in other tab: "
+                        (confirm-nonexistent-file-or-buffer)))
+  (let ((value (find-file-noselect filename nil nil wildcards)))
+    (if (listp value)
+       (progn
+         (setq value (nreverse value))
+         (switch-to-buffer-other-tab (car value))
+         (mapc 'switch-to-buffer (cdr value))
+         value)
+      (switch-to-buffer-other-tab value))))
+
+(define-key ctl-x-6-map "2" 'tab-bar-add-tab)
+(define-key ctl-x-6-map "b" 'switch-to-buffer-other-tab)
+(define-key ctl-x-6-map "f" 'find-file-other-tab)
+(define-key ctl-x-6-map "\C-f" 'find-file-other-tab)
+
+
+(provide 'tab-bar)
+
+;;; tab-bar.el ends here
diff --git a/lisp/tab-line.el b/lisp/tab-line.el
new file mode 100644
index 0000000..addd045
--- /dev/null
+++ b/lisp/tab-line.el
@@ -0,0 +1,264 @@
+;;; tab-line.el --- window-local tab line with window buffers -*- 
lexical-binding: t; -*-
+
+;; Copyright (C) 2019 Free Software Foundation, Inc.
+
+;; Author: Juri Linkov <address@hidden>
+;; Keywords: windows tabs
+;; Maintainer: address@hidden
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; To enable this mode, run `M-x global-tab-line-mode'.
+
+;;; Code:
+
+(require 'seq) ; tab-line.el is not pre-loaded so it's safe to use it here
+
+
+(defgroup tab-line nil
+  "Window-local tab line."
+  :group 'convenience
+  :version "27.1")
+
+(defgroup tab-line-faces nil
+  "Faces used in the tab line."
+  :group 'tab-line
+  :group 'faces
+  :version "27.1")
+
+(defface tab-line
+  '((default :inherit header-line))
+  "Tab line face."
+  :version "27.1"
+  :group 'tab-line-faces)
+
+(defface tab-line-highlight
+  '((default :inherit tab-line-tab))
+  "Tab line face for highlighting."
+  :version "27.1"
+  :group 'tab-line-faces)
+
+(defface tab-line-close-highlight
+  '((t :foreground "red"))
+  "Tab line face for highlighting."
+  :version "27.1"
+  :group 'tab-line-faces)
+
+(defface tab-line-tab
+  '((((class color) (min-colors 88))
+     :box (:line-width -1 :style pressed-button)
+     :background "white" :foreground "black")
+    (t
+     :inverse-video t))
+  "Tab line face for selected tab."
+  :version "27.1"
+  :group 'tab-line-faces)
+
+(defface tab-line-tab-inactive
+  '((default
+     :inherit tab-line)
+    (((class color) (min-colors 88) (background light))
+     :weight light
+     :box (:line-width -1 :color "grey75" :style released-button)
+     :foreground "grey20" :background "grey90")
+    (((class color) (min-colors 88) (background dark) )
+     :weight light
+     :box (:line-width -1 :color "grey40" :style released-button)
+     :foreground "grey80" :background "grey30"))
+  "Tab line face for non-selected tabs."
+  :version "27.1"
+  :group 'tab-line-faces)
+
+(defvar tab-line-tab-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map [tab-line mouse-1] 'tab-line-select-tab)
+    (define-key map [tab-line mouse-2] 'tab-line-select-tab)
+    (define-key map [tab-line mouse-4] 'tab-line-switch-to-prev-tab)
+    (define-key map [tab-line mouse-5] 'tab-line-switch-to-next-tab)
+    (define-key map "\C-m" 'tab-line-select-tab)
+    (define-key map [follow-link] 'mouse-face)
+    map)
+  "Local keymap for `tab-line-mode' window tabs.")
+
+(defvar tab-line-add-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map [tab-line mouse-1] 'tab-line-add-tab)
+    (define-key map [tab-line mouse-2] 'tab-line-add-tab)
+    (define-key map "\C-m" 'tab-line-add-tab)
+    (define-key map [follow-link] 'mouse-face)
+    map)
+  "Local keymap to add `tab-line-mode' window tabs.")
+
+(defvar tab-line-tab-close-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map [tab-line mouse-1] 'tab-line-close-tab)
+    (define-key map [tab-line mouse-2] 'tab-line-close-tab)
+    (define-key map [follow-link] 'mouse-face)
+    map)
+  "Local keymap to close `tab-line-mode' window tabs.")
+
+(defvar tab-line-separator " ")
+(defvar tab-line-tab-name-ellipsis (if (char-displayable-p ?…) "…" "..."))
+(defvar tab-line-tab-name-add      (if (char-displayable-p ?➕) "➕" "[+]"))
+(defvar tab-line-tab-name-close    (if (char-displayable-p ?⮿) "⮿" "[x]"))
+
+
+(defun tab-line-tab-name (buffer &optional buffers)
+  "Generate tab name from BUFFER.
+Reduce tab width proportionally to space taken by other tabs."
+  (let ((tab-name (buffer-name buffer))
+        (limit (when buffers
+                 (max 1 (- (/ (window-width) (length buffers)) 3)))))
+    (if (or (not limit) (< (length tab-name) limit))
+        tab-name
+      (concat tab-line-tab-name-ellipsis (substring tab-name (- limit))))))
+
+(defun tab-line-format ()
+  "Template for displaying tab line for selected window."
+  (let* ((window (selected-window))
+         (buffer (window-buffer window))
+         (next-buffers (seq-remove (lambda (b) (eq b buffer))
+                                   (window-next-buffers window)))
+         (prev-buffers (seq-remove (lambda (b) (eq b buffer))
+                                   (mapcar #'car (window-prev-buffers 
window))))
+         ;; Remove next-buffers from prev-buffers
+         (prev-buffers (seq-difference prev-buffers next-buffers))
+         (buffers (append (reverse prev-buffers)
+                          (list buffer)
+                          next-buffers))
+         (buffers (seq-filter #'buffer-live-p buffers)))
+    (append
+     (mapcar
+      (lambda (b)
+        (format "%s%s%s"
+                tab-line-separator
+                (apply 'propertize (tab-line-tab-name b buffers)
+                       `(
+                         help-echo "Click to visit tab"
+                         buffer ,b
+                         face ,(if (eq b buffer)
+                                   'tab-line-tab
+                                 'tab-line-tab-inactive)
+                         mouse-face tab-line-highlight
+                         keymap ,tab-line-tab-map))
+                (apply 'propertize tab-line-tab-name-close
+                       `(
+                         help-echo "Click to close tab"
+                         buffer ,b
+                         face ,(if (eq b buffer)
+                                   'tab-line-tab
+                                 'tab-line-tab-inactive)
+                         mouse-face tab-line-close-highlight
+                         keymap ,tab-line-tab-close-map))))
+      buffers)
+     (list (format "%s%s"
+                   tab-line-separator
+                   (apply 'propertize tab-line-tab-name-add
+                          `(
+                            help-echo "Click to add tab"
+                            face tab-line-tab-inactive
+                            mouse-face tab-line-highlight
+                            keymap ,tab-line-add-map)))))))
+
+
+(defun tab-line-add-tab (&optional e)
+  (interactive "e")
+  ;; Maybe (buffer-menu-open)
+  (mouse-buffer-menu e))
+
+(defun tab-line-select-tab (&optional e)
+  "Switch to the selected tab.
+This command maintains the original order of prev/next buffers.
+So for example, switching to a previous tab is equivalent to
+using the `previous-buffer' command."
+  (interactive "e")
+  (let* ((posnp (event-start e))
+         (window (posn-window posnp))
+         (buffer (get-pos-property 1 'buffer (car (posn-string posnp))))
+         (window-buffer (window-buffer window))
+         (next-buffers (seq-remove (lambda (b) (eq b window-buffer))
+                                   (window-next-buffers window)))
+         (prev-buffers (seq-remove (lambda (b) (eq b window-buffer))
+                                   (mapcar #'car (window-prev-buffers 
window))))
+         ;; Remove next-buffers from prev-buffers
+         (prev-buffers (seq-difference prev-buffers next-buffers)))
+    (cond
+     ((memq buffer next-buffers)
+      (dotimes (_ (1+ (seq-position next-buffers buffer)))
+        (switch-to-next-buffer window)))
+     ((memq buffer prev-buffers)
+      (dotimes (_ (1+ (seq-position prev-buffers buffer)))
+        (switch-to-prev-buffer window)))
+     (t
+      (switch-to-buffer buffer)))))
+
+(defun tab-line-switch-to-prev-tab (&optional e)
+  "Switch to the previous tab."
+  (interactive "e")
+  (switch-to-prev-buffer (posn-window (event-start e))))
+
+(defun tab-line-switch-to-next-tab (&optional e)
+  "Switch to the next tab."
+  (interactive "e")
+  (switch-to-next-buffer (posn-window (event-start e))))
+
+(defun tab-line-close-tab (&optional e)
+  "Close the selected tab."
+  (interactive "e")
+  (let* ((posnp (event-start e))
+         (window (posn-window posnp))
+         (buffer (get-pos-property 1 'buffer (car (posn-string posnp)))))
+    (with-selected-window window
+      (if (eq buffer (current-buffer))
+          (bury-buffer)
+        (set-window-prev-buffers nil (assq-delete-all buffer 
(window-prev-buffers)))
+        (set-window-next-buffers nil (delq buffer (window-next-buffers))))
+      (force-mode-line-update))))
+
+
+(defvar tab-line-format '(:eval (tab-line-format)))
+
+;;;###autoload
+(define-minor-mode global-tab-line-mode
+  "Display window-local tab line."
+  :group 'tab-line
+  :type 'boolean
+  :global t
+  :init-value nil
+  :initialize (lambda (sym val)
+                (custom-initialize-default sym val)
+                (when global-tab-line-mode
+                  (add-hook 'pre-redisplay-functions 
#'tab-line-update-window-parameter)))
+  (if global-tab-line-mode
+      (progn
+        (add-hook 'pre-redisplay-functions #'tab-line-update-window-parameter)
+        (force-mode-line-update))
+    (remove-hook 'pre-redisplay-functions #'tab-line-update-window-parameter)
+    (walk-windows (lambda (w) (tab-line-update-window-parameter w)) t)))
+
+(defun tab-line-update-window-parameter (window)
+  (let* ((name 'tab-line-format)
+         (value (window-parameter window name))
+         (active global-tab-line-mode))
+    (when (xor value active)
+      (set-window-parameter
+       window name (unless value tab-line-format)))))
+
+
+(provide 'tab-line)
+;;; tab-line.el ends here
diff --git a/lisp/window.el b/lisp/window.el
index cf73315..2784c2d 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -1419,7 +1419,10 @@ dumping to it."
        (format "frame text pixel: %s x %s   cols/lines: %s x %s\n"
               (frame-text-width frame) (frame-text-height frame)
               (frame-text-cols frame) (frame-text-lines frame))
-       (format "tool: %s  scroll: %s/%s  fringe: %s  border: %s  right: %s  
bottom: %s\n\n"
+       (format "tab: %s  tool: %s  scroll: %s/%s  fringe: %s  border: %s  
right: %s  bottom: %s\n\n"
+              (if (fboundp 'tab-bar-height)
+                  (tab-bar-height frame t)
+                "0")
               (if (fboundp 'tool-bar-height)
                   (tool-bar-height frame t)
                 "0")
diff --git a/src/buffer.c b/src/buffer.c
index 62a3d66..ad9feee 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1323,7 +1323,7 @@ No argument or nil as argument means use current buffer 
as BUFFER.  */)
 DEFUN ("force-mode-line-update", Fforce_mode_line_update,
        Sforce_mode_line_update, 0, 1, 0,
        doc: /* Force redisplay of the current buffer's mode line and header 
line.
-With optional non-nil ALL, force redisplay of all mode lines and
+With optional non-nil ALL, force redisplay of all mode lines, tab lines and
 header lines.  This function also forces recomputation of the
 menu bar menus and the frame title.  */)
      (Lisp_Object all)
diff --git a/src/dispextern.h b/src/dispextern.h
index 05f199f..02aba05 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -166,6 +166,7 @@ enum window_part
   ON_MODE_LINE,
   ON_VERTICAL_BORDER,
   ON_HEADER_LINE,
+  ON_TAB_LINE,
   ON_LEFT_FRINGE,
   ON_RIGHT_FRINGE,
   ON_LEFT_MARGIN,
@@ -762,6 +763,9 @@ struct glyph_matrix
      which do their own scrolling.  */
   bool_bf no_scrolling_p : 1;
 
+  /* True means window displayed in this matrix has a tab line.  */
+  bool_bf tab_line_p : 1;
+
   /* True means window displayed in this matrix has a header
      line.  */
   bool_bf header_line_p : 1;
@@ -1001,9 +1005,12 @@ struct glyph_row
      implies that the row doesn't have marginal areas.  */
   bool_bf full_width_p : 1;
 
-  /* True means row is a mode or header-line.  */
+  /* True means row is a mode or header/tab-line.  */
   bool_bf mode_line_p : 1;
 
+  /* True means row is a tab-line.  */
+  bool_bf tab_line_p : 1;
+
   /* True in a current row means this row is overlapped by another row.  */
   bool_bf overlapped_p : 1;
 
@@ -1084,16 +1091,25 @@ struct glyph_row *matrix_row (struct glyph_matrix *, 
int);
 #define MATRIX_MODE_LINE_ROW(MATRIX) \
      ((MATRIX)->rows + (MATRIX)->nrows - 1)
 
-/* Return a pointer to the row reserved for the header line in MATRIX.
+/* Return a pointer to the row reserved for the tab line in MATRIX.
    This is always the first row in MATRIX because that's the only
    way that works in frame-based redisplay.  */
 
-#define MATRIX_HEADER_LINE_ROW(MATRIX) (MATRIX)->rows
+#define MATRIX_TAB_LINE_ROW(MATRIX) (MATRIX)->rows
+
+/* Return a pointer to the row reserved for the header line in MATRIX.
+   This is always the second row in MATRIX because that's the only
+   way that works in frame-based redisplay.  */
+
+#define MATRIX_HEADER_LINE_ROW(MATRIX) \
+     ((MATRIX)->tab_line_p ? ((MATRIX)->rows + 1) : (MATRIX)->rows)
 
 /* Return a pointer to first row in MATRIX used for text display.  */
 
 #define MATRIX_FIRST_TEXT_ROW(MATRIX) \
-     ((MATRIX)->rows->mode_line_p ? (MATRIX)->rows + 1 : (MATRIX)->rows)
+  ((MATRIX)->rows->mode_line_p ?                                        \
+   (((MATRIX)->rows + 1)->mode_line_p ?                                 \
+    (MATRIX)->rows + 2 : (MATRIX)->rows + 1) : (MATRIX)->rows)
 
 /* Return a pointer to the first glyph in the text area of a row.
    MATRIX is the glyph matrix accessed, and ROW is the row index in
@@ -1162,7 +1178,7 @@ struct glyph_row *matrix_row (struct glyph_matrix *, int);
   ((ROW)->height != (ROW)->visible_height)
 
 #define MR_PARTIALLY_VISIBLE_AT_TOP(W, ROW)  \
-  ((ROW)->y < WINDOW_HEADER_LINE_HEIGHT ((W)))
+  ((ROW)->y < (WINDOW_TAB_LINE_HEIGHT ((W)) + WINDOW_HEADER_LINE_HEIGHT ((W))))
 
 #define MR_PARTIALLY_VISIBLE_AT_BOTTOM(W, ROW)  \
   (((ROW)->y + (ROW)->height - (ROW)->extra_line_spacing) \
@@ -1433,6 +1449,15 @@ struct glyph_string
       ? MATRIX_HEADER_LINE_ROW (MATRIX)->height        \
       : 0)
 
+/* Return the height of the tab line in glyph matrix MATRIX, or zero
+   if not known.  This macro is called under circumstances where
+   MATRIX might not have been allocated yet.  */
+
+#define MATRIX_TAB_LINE_HEIGHT(MATRIX) \
+     ((MATRIX) && (MATRIX)->rows               \
+      ? MATRIX_TAB_LINE_ROW (MATRIX)->height   \
+      : 0)
+
 /* Return the desired face id for the mode line of a window, depending
    on whether the window is selected or not, or if the window is the
    scrolling window for the currently active minibuffer window.
@@ -1485,6 +1510,19 @@ struct glyph_string
         : estimate_mode_line_height                            \
             (XFRAME (W->frame), HEADER_LINE_FACE_ID))))
 
+/* Return the current height of the tab line of window W.  If not known
+   from W->tab_line_height, look at W's current glyph matrix, or return
+   an estimation based on the height of the font of the face `tab-line'.  */
+
+#define CURRENT_TAB_LINE_HEIGHT(W)                             \
+  (W->tab_line_height >= 0                                     \
+   ? W->tab_line_height                                                \
+   : (W->tab_line_height                                       \
+      = (MATRIX_TAB_LINE_HEIGHT (W->current_matrix)            \
+        ? MATRIX_TAB_LINE_HEIGHT (W->current_matrix)           \
+        : estimate_mode_line_height                            \
+            (XFRAME (W->frame), TAB_LINE_FACE_ID))))
+
 /* Return the height of the desired mode line of window W.  */
 
 #define DESIRED_MODE_LINE_HEIGHT(W) \
@@ -1495,6 +1533,11 @@ struct glyph_string
 #define DESIRED_HEADER_LINE_HEIGHT(W) \
      MATRIX_HEADER_LINE_HEIGHT ((W)->desired_matrix)
 
+/* Return the height of the desired tab line of window W.  */
+
+#define DESIRED_TAB_LINE_HEIGHT(W) \
+     MATRIX_TAB_LINE_HEIGHT ((W)->desired_matrix)
+
 /* Return proper value to be used as baseline offset of font that has
    ASCENT and DESCENT to draw characters by the font at the vertical
    center of the line of frame F.
@@ -1780,6 +1823,8 @@ enum face_id
   WINDOW_DIVIDER_FIRST_PIXEL_FACE_ID,
   WINDOW_DIVIDER_LAST_PIXEL_FACE_ID,
   INTERNAL_BORDER_FACE_ID,
+  TAB_BAR_FACE_ID,
+  TAB_LINE_FACE_ID,
   BASIC_FACE_ID_SENTINEL
 };
 
@@ -2283,6 +2328,9 @@ struct it
   /* True means multibyte characters are enabled.  */
   bool_bf multibyte_p : 1;
 
+  /* True means window has a tab line at its top.  */
+  bool_bf tab_line_p : 1;
+
   /* True means window has a mode line at its top.  */
   bool_bf header_line_p : 1;
 
@@ -3130,6 +3178,81 @@ struct image_cache
 
 
 /***********************************************************************
+                              Tab-bars
+ ***********************************************************************/
+
+/* Enumeration defining where to find tab-bar item information in
+   tab-bar items vectors stored with frames.  Each tab-bar item
+   occupies TAB_BAR_ITEM_NSLOTS elements in such a vector.  */
+
+enum tab_bar_item_idx
+{
+  /* The key of the tab-bar item.  Used to remove items when a binding
+     for `undefined' is found.  */
+  TAB_BAR_ITEM_KEY,
+
+  /* Non-nil if item is enabled.  */
+  TAB_BAR_ITEM_ENABLED_P,
+
+  /* Non-nil if item is selected (pressed).  */
+  TAB_BAR_ITEM_SELECTED_P,
+
+  /* Caption.  */
+  TAB_BAR_ITEM_CAPTION,
+
+  /* Image(s) to display.  This is either a single image specification
+     or a vector of specifications.  */
+  TAB_BAR_ITEM_IMAGES,
+
+  /* The binding.  */
+  TAB_BAR_ITEM_BINDING,
+
+  /* Button type.  One of nil (default button), t (a separator),
+     `:radio', or `:toggle'.  The latter two currently do nothing.  */
+  TAB_BAR_ITEM_TYPE,
+
+  /* Help string.  */
+  TAB_BAR_ITEM_HELP,
+
+  /* Icon file name of right to left image when an RTL locale is used.  */
+  TAB_BAR_ITEM_RTL_IMAGE,
+
+  /* Label to show when text labels are enabled.  */
+  TAB_BAR_ITEM_LABEL,
+
+  /* If we shall show the label only below the icon and not beside it.  */
+  TAB_BAR_ITEM_VERT_ONLY,
+
+  /* Sentinel = number of slots in tab_bar_items occupied by one
+     tab-bar item.  */
+  TAB_BAR_ITEM_NSLOTS
+};
+
+
+/* An enumeration for the different images that can be specified
+   for a tab-bar item.  */
+
+enum tab_bar_item_image
+{
+  TAB_BAR_IMAGE_ENABLED_SELECTED,
+  TAB_BAR_IMAGE_ENABLED_DESELECTED,
+  TAB_BAR_IMAGE_DISABLED_SELECTED,
+  TAB_BAR_IMAGE_DISABLED_DESELECTED
+};
+
+#define DEFAULT_TAB_BAR_LABEL_SIZE 14
+
+/* Default values of the above variables.  */
+
+#define DEFAULT_TAB_BAR_BUTTON_MARGIN 4
+#define DEFAULT_TAB_BAR_BUTTON_RELIEF 1
+
+/* The height in pixels of the default tab-bar images.  */
+
+#define DEFAULT_TAB_BAR_IMAGE_HEIGHT 18
+
+
+/***********************************************************************
                               Tool-bars
  ***********************************************************************/
 
@@ -3285,6 +3408,7 @@ extern bool help_echo_showing_p;
 extern Lisp_Object help_echo_string, help_echo_window;
 extern Lisp_Object help_echo_object, previous_help_echo_string;
 extern ptrdiff_t help_echo_pos;
+extern int last_tab_bar_item;
 extern int last_tool_bar_item;
 extern void reseat_at_previous_visible_line_start (struct it *);
 extern Lisp_Object lookup_glyphless_char_display (int, struct it *);
@@ -3332,6 +3456,8 @@ extern void get_glyph_string_clip_rect (struct 
glyph_string *,
                                         NativeRectangle *nr);
 extern Lisp_Object find_hot_spot (Lisp_Object, int, int);
 
+extern void handle_tab_bar_click (struct frame *,
+                                   int, int, bool, int);
 extern void handle_tool_bar_click (struct frame *,
                                    int, int, bool, int);
 
diff --git a/src/dispnew.c b/src/dispnew.c
index 799ef2b..3e1dad1 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -80,7 +80,7 @@ static void adjust_decode_mode_spec_buffer (struct frame *);
 static void fill_up_glyph_row_with_spaces (struct glyph_row *);
 static void clear_window_matrices (struct window *, bool);
 static void fill_up_glyph_row_area_with_spaces (struct glyph_row *, int);
-static int scrolling_window (struct window *, bool);
+static int scrolling_window (struct window *, int);
 static bool update_window_line (struct window *, int, bool *);
 static void mirror_make_current (struct window *, int);
 #ifdef GLYPH_DEBUG
@@ -366,6 +366,8 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
   int i;
   int new_rows;
   bool marginal_areas_changed_p = 0;
+  bool tab_line_changed_p = 0;
+  bool tab_line_p = 0;
   bool header_line_changed_p = 0;
   bool header_line_p = 0;
   int left = -1, right = -1;
@@ -377,9 +379,13 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
     {
       window_box (w, ANY_AREA, 0, 0, &window_width, &window_height);
 
+      tab_line_p = window_wants_tab_line (w);
+      tab_line_changed_p = tab_line_p != matrix->tab_line_p;
+
       header_line_p = window_wants_header_line (w);
       header_line_changed_p = header_line_p != matrix->header_line_p;
     }
+  matrix->tab_line_p = tab_line_p;
   matrix->header_line_p = header_line_p;
 
   /* If POOL is null, MATRIX is a window matrix for window-based redisplay.
@@ -397,6 +403,7 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
 
       if (!marginal_areas_changed_p
          && !XFRAME (w->frame)->fonts_changed
+         && !tab_line_changed_p
          && !header_line_changed_p
          && matrix->window_pixel_left == WINDOW_LEFT_PIXEL_EDGE (w)
          && matrix->window_pixel_top == WINDOW_TOP_PIXEL_EDGE (w)
@@ -448,7 +455,9 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
          if (w == NULL
              || (row == matrix->rows + dim.height - 1
                  && window_wants_mode_line (w))
-             || (row == matrix->rows && matrix->header_line_p))
+             || (row == matrix->rows && matrix->tab_line_p)
+             || (row == matrix->rows && !matrix->tab_line_p && 
matrix->header_line_p)
+             || (row == (matrix->rows + 1) && matrix->tab_line_p && 
matrix->header_line_p))
            {
              row->glyphs[TEXT_AREA]
                = row->glyphs[LEFT_MARGIN_AREA];
@@ -478,6 +487,7 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
         Allocate glyph memory from the heap.  */
       if (dim.width > matrix->matrix_w
          || new_rows
+         || tab_line_changed_p
          || header_line_changed_p
          || marginal_areas_changed_p)
        {
@@ -493,7 +503,9 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
              /* The mode line, if displayed, never has marginal areas.  */
              if ((row == matrix->rows + dim.height - 1
                   && !(w && window_wants_mode_line (w)))
-                 || (row == matrix->rows && matrix->header_line_p))
+                 || (row == matrix->rows && matrix->tab_line_p)
+                 || (row == matrix->rows && !matrix->tab_line_p && 
matrix->header_line_p)
+                 || (row == (matrix->rows + 1) && matrix->tab_line_p && 
matrix->header_line_p))
                {
                  row->glyphs[TEXT_AREA]
                    = row->glyphs[LEFT_MARGIN_AREA];
@@ -539,6 +551,7 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int x, int y
             upper window).  Invalidate all rows that are no longer part
             of the window.  */
          if (!marginal_areas_changed_p
+             && !tab_line_changed_p
              && !header_line_changed_p
              && new_rows == 0
              && dim.width == matrix->matrix_w
@@ -728,7 +741,7 @@ shift_glyph_matrix (struct window *w, struct glyph_matrix 
*matrix, int start, in
   eassert (start >= 0 && start < matrix->nrows);
   eassert (end >= 0 && end <= matrix->nrows);
 
-  min_y = WINDOW_HEADER_LINE_HEIGHT (w);
+  min_y = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w);
   max_y = WINDOW_BOX_HEIGHT_NO_MODE_LINE (w);
 
   for (; start < end; ++start)
@@ -767,6 +780,12 @@ clear_current_matrices (register struct frame *f)
     clear_glyph_matrix (XWINDOW (f->menu_bar_window)->current_matrix);
 #endif
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  /* Clear the matrix of the tab-bar window, if any.  */
+  if (WINDOWP (f->tab_bar_window))
+    clear_glyph_matrix (XWINDOW (f->tab_bar_window)->current_matrix);
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   /* Clear the matrix of the tool-bar window, if any.  */
   if (WINDOWP (f->tool_bar_window))
@@ -792,6 +811,11 @@ clear_desired_matrices (register struct frame *f)
     clear_glyph_matrix (XWINDOW (f->menu_bar_window)->desired_matrix);
 #endif
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  if (WINDOWP (f->tab_bar_window))
+    clear_glyph_matrix (XWINDOW (f->tab_bar_window)->desired_matrix);
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   if (WINDOWP (f->tool_bar_window))
     clear_glyph_matrix (XWINDOW (f->tool_bar_window)->desired_matrix);
@@ -857,7 +881,7 @@ blank_row (struct window *w, struct glyph_row *row, int y)
 {
   int min_y, max_y;
 
-  min_y = WINDOW_HEADER_LINE_HEIGHT (w);
+  min_y = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w);
   max_y = WINDOW_BOX_HEIGHT_NO_MODE_LINE (w);
 
   clear_glyph_row (row);
@@ -1062,7 +1086,7 @@ find_glyph_row_slice (struct glyph_matrix *window_matrix,
    call to this function really clears it.  In addition, this function
    makes sure the marginal areas of ROW are in sync with the window's
    display margins.  MODE_LINE_P non-zero means we are preparing a
-   glyph row for header line or mode line.  */
+   glyph row for tab/header line or mode line.  */
 
 void
 prepare_desired_row (struct window *w, struct glyph_row *row, bool mode_line_p)
@@ -1077,11 +1101,11 @@ prepare_desired_row (struct window *w, struct glyph_row 
*row, bool mode_line_p)
     }
   if (mode_line_p)
     {
-      /* Mode and header lines, if displayed, never have marginal
+      /* Mode and header/tab lines, if displayed, never have marginal
         areas.  If we are called with MODE_LINE_P non-zero, we are
-        displaying the mode/header line in this window, and so the
+        displaying the mode/header/tab line in this window, and so the
         marginal areas of this glyph row should be eliminated.  This
-        is needed when the mode/header line is switched on in a
+        is needed when the mode/header/tab line is switched on in a
         window that has display margins.  */
       if (w->left_margin_cols > 0)
        row->glyphs[TEXT_AREA] = row->glyphs[LEFT_MARGIN_AREA];
@@ -1099,7 +1123,7 @@ prepare_desired_row (struct window *w, struct glyph_row 
*row, bool mode_line_p)
 
       /* Make sure the marginal areas of this row are in sync with
         what the window wants, when the row actually displays text
-        and not header/mode line.  */
+        and not tab/header/mode line.  */
       if (w->left_margin_cols > 0
          && (left != row->glyphs[TEXT_AREA] - row->glyphs[LEFT_MARGIN_AREA]))
        row->glyphs[TEXT_AREA] = row->glyphs[LEFT_MARGIN_AREA] + left;
@@ -1708,8 +1732,8 @@ required_matrix_height (struct window *w)
              /* One partially visible line at the top and
                 bottom of the window.  */
              + 2
-             /* 2 for header and mode line.  */
-             + 2);
+             /* 3 for tab, header and mode line.  */
+             + 3);
     }
 #endif /* HAVE_WINDOW_SYSTEM */
 
@@ -1862,6 +1886,7 @@ fake_current_matrices (Lisp_Object window)
                                        - r->used[LEFT_MARGIN_AREA]
                                        - r->used[RIGHT_MARGIN_AREA]);
                  r->mode_line_p = 0;
+                 r->tab_line_p = 0;
                }
            }
        }
@@ -2106,6 +2131,36 @@ adjust_frame_glyphs_for_window_redisplay (struct frame 
*f)
   }
 #endif
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  {
+    /* Allocate/ reallocate matrices of the tab bar window.  If we
+       don't have a tab bar window yet, make one.  */
+    struct window *w;
+    if (NILP (f->tab_bar_window))
+      {
+       Lisp_Object frame;
+       fset_tab_bar_window (f, make_window ());
+       w = XWINDOW (f->tab_bar_window);
+       XSETFRAME (frame, f);
+       wset_frame (w, frame);
+       w->pseudo_window_p = 1;
+      }
+    else
+      w = XWINDOW (f->tab_bar_window);
+
+    w->pixel_left = 0;
+    w->left_col = 0;
+    w->pixel_top = FRAME_MENU_BAR_HEIGHT (f);
+    w->top_line = FRAME_MENU_BAR_LINES (f);
+    w->total_cols = FRAME_TOTAL_COLS (f);
+    w->pixel_width = (FRAME_PIXEL_WIDTH (f)
+                      - 2 * FRAME_INTERNAL_BORDER_WIDTH (f));
+    w->total_lines = FRAME_TAB_BAR_LINES (f);
+    w->pixel_height = FRAME_TAB_BAR_HEIGHT (f);
+    allocate_matrices_for_window_redisplay (w);
+  }
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   {
     /* Allocate/ reallocate matrices of the tool bar window.  If we
@@ -2125,8 +2180,8 @@ adjust_frame_glyphs_for_window_redisplay (struct frame *f)
 
     w->pixel_left = 0;
     w->left_col = 0;
-    w->pixel_top = FRAME_MENU_BAR_HEIGHT (f);
-    w->top_line = FRAME_MENU_BAR_LINES (f);
+    w->pixel_top = FRAME_MENU_BAR_HEIGHT (f) + FRAME_TAB_BAR_HEIGHT (f);
+    w->top_line = FRAME_MENU_BAR_LINES (f) + FRAME_TAB_BAR_LINES (f);
     w->total_cols = FRAME_TOTAL_COLS (f);
     w->pixel_width = (FRAME_PIXEL_WIDTH (f)
                       - 2 * FRAME_INTERNAL_BORDER_WIDTH (f));
@@ -2188,6 +2243,18 @@ free_glyphs (struct frame *f)
        }
 #endif
 
+#if defined (HAVE_WINDOW_SYSTEM)
+      /* Free the tab bar window and its glyph matrices.  */
+      if (!NILP (f->tab_bar_window))
+       {
+         struct window *w = XWINDOW (f->tab_bar_window);
+         free_glyph_matrix (w->desired_matrix);
+         free_glyph_matrix (w->current_matrix);
+         w->desired_matrix = w->current_matrix = NULL;
+         fset_tab_bar_window (f, Qnil);
+       }
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
       /* Free the tool bar window and its glyph matrices.  */
       if (!NILP (f->tool_bar_window))
@@ -3082,6 +3149,29 @@ update_frame (struct frame *f, bool force_p, bool 
inhibit_hairy_id_p)
        update_window (XWINDOW (f->menu_bar_window), true);
 #endif
 
+#if defined (HAVE_WINDOW_SYSTEM)
+      /* Update the tab-bar window, if present.  */
+      if (WINDOWP (f->tab_bar_window))
+       {
+         struct window *w = XWINDOW (f->tab_bar_window);
+
+         /* Update tab-bar window.  */
+         if (w->must_be_updated_p)
+           {
+             Lisp_Object tem;
+
+             update_window (w, true);
+             w->must_be_updated_p = false;
+
+             /* Swap tab-bar strings.  We swap because we want to
+                reuse strings.  */
+             tem = f->current_tab_bar_string;
+             fset_current_tab_bar_string (f, f->desired_tab_bar_string);
+             fset_desired_tab_bar_string (f, tem);
+           }
+       }
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
       /* Update the tool-bar window, if present.  */
       if (WINDOWP (f->tool_bar_window))
@@ -3408,6 +3498,7 @@ update_window (struct window *w, bool force_p)
     {
       struct glyph_row *row, *end;
       struct glyph_row *mode_line_row;
+      struct glyph_row *tab_line_row;
       struct glyph_row *header_line_row;
       int yb;
       bool changed_p = 0, mouse_face_overwritten_p = 0;
@@ -3420,6 +3511,16 @@ update_window (struct window *w, bool force_p)
       row = MATRIX_ROW (desired_matrix, 0);
       end = MATRIX_MODE_LINE_ROW (desired_matrix);
 
+      /* Take note of the tab line, if there is one.  We will
+        update it below, after updating all of the window's lines.  */
+      if (row->mode_line_p && row->tab_line_p)
+       {
+         tab_line_row = row;
+         ++row;
+       }
+      else
+       tab_line_row = NULL;
+
       /* Take note of the header line, if there is one.  We will
         update it below, after updating all of the window's lines.  */
       if (row->mode_line_p)
@@ -3449,7 +3550,7 @@ update_window (struct window *w, bool force_p)
       /* Try reusing part of the display by copying.  */
       if (row < end && !desired_matrix->no_scrolling_p)
        {
-         int rc = scrolling_window (w, header_line_row != NULL);
+         int rc = scrolling_window (w, (tab_line_row != NULL ? 1 : 0) + 
(header_line_row != NULL ? 1 : 0));
          if (rc < 0)
            {
              /* All rows were found to be equal.  */
@@ -3501,13 +3602,22 @@ update_window (struct window *w, bool force_p)
 
     set_cursor:
 
+      /* Update the tab line after scrolling because a new tab
+        line would otherwise overwrite lines at the top of the window
+        that can be scrolled.  */
+      if (tab_line_row && tab_line_row->enabled_p)
+       {
+         tab_line_row->y = 0;
+         update_window_line (w, 0, &mouse_face_overwritten_p);
+       }
+
       /* Update the header line after scrolling because a new header
         line would otherwise overwrite lines at the top of the window
         that can be scrolled.  */
       if (header_line_row && header_line_row->enabled_p)
        {
-         header_line_row->y = 0;
-         update_window_line (w, 0, &mouse_face_overwritten_p);
+         header_line_row->y = tab_line_row ? CURRENT_TAB_LINE_HEIGHT (w) : 0;
+         update_window_line (w, tab_line_row ? 1 : 0, 
&mouse_face_overwritten_p);
        }
 
       /* Fix the appearance of overlapping/overlapped rows.  */
@@ -4178,7 +4288,7 @@ add_row_entry (struct glyph_row *row)
    1   if we did scroll.  */
 
 static int
-scrolling_window (struct window *w, bool header_line_p)
+scrolling_window (struct window *w, int tab_line_p)
 {
   struct glyph_matrix *desired_matrix = w->desired_matrix;
   struct glyph_matrix *current_matrix = w->current_matrix;
@@ -4191,7 +4301,7 @@ scrolling_window (struct window *w, bool header_line_p)
   struct redisplay_interface *rif = FRAME_RIF (XFRAME (WINDOW_FRAME (w)));
 
   /* Skip over rows equal at the start.  */
-  for (i = header_line_p; i < current_matrix->nrows - 1; ++i)
+  for (i = tab_line_p; i < current_matrix->nrows - 1; ++i)
     {
       struct glyph_row *d = MATRIX_ROW (desired_matrix, i);
       struct glyph_row *c = MATRIX_ROW (current_matrix, i);
@@ -5318,7 +5428,7 @@ buffer_posn_from_coords (struct window *w, int *x, int 
*y, struct display_pos *p
      start position, i.e. it excludes the header-line row, but
      MATRIX_ROW includes the header-line row.  Adjust for a possible
      header-line row.  */
-  it_vpos = it.vpos + window_wants_header_line (w);
+  it_vpos = it.vpos + window_wants_header_line (w) + window_wants_tab_line (w);
   if (it_vpos < w->current_matrix->nrows
       && (row = MATRIX_ROW (w->current_matrix, it_vpos),
          row->enabled_p))
@@ -5382,6 +5492,8 @@ mode_line_string (struct window *w, enum window_part part,
 
   if (part == ON_MODE_LINE)
     row = MATRIX_MODE_LINE_ROW (w->current_matrix);
+  else if (part == ON_TAB_LINE)
+    row = MATRIX_TAB_LINE_ROW (w->current_matrix);
   else
     row = MATRIX_HEADER_LINE_ROW (w->current_matrix);
   y0 = *y - row->y;
diff --git a/src/frame.c b/src/frame.c
index 1d42d0c..43bd5c2 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -69,6 +69,9 @@ static struct frame *last_nonminibuf_frame;
 /* False means there are no visible garbaged frames.  */
 bool frame_garbaged;
 
+/* The default tab bar height for future frames.  */
+int frame_default_tab_bar_height;
+
 /* The default tool bar height for future frames.  */
 #ifdef HAVE_EXT_TOOL_BAR
 enum { frame_default_tool_bar_height = 0 };
@@ -719,6 +722,15 @@ adjust_frame_size (struct frame *f, int new_width, int 
new_height, int inhibit,
       if ((FRAME_TERMCAP_P (f) && !pretend) || FRAME_MSDOS_P (f))
        FrameCols (FRAME_TTY (f)) = new_cols;
 
+#if defined (HAVE_WINDOW_SYSTEM)
+      if (WINDOWP (f->tab_bar_window))
+       {
+         XWINDOW (f->tab_bar_window)->pixel_width = new_windows_width;
+         XWINDOW (f->tab_bar_window)->total_cols
+           = new_windows_width / unit_width;
+       }
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
       if (WINDOWP (f->tool_bar_window))
        {
@@ -838,6 +850,8 @@ make_frame (bool mini_p)
   f->after_make_frame = false;
   f->inhibit_horizontal_resize = false;
   f->inhibit_vertical_resize = false;
+  f->tab_bar_redisplayed = false;
+  f->tab_bar_resized = false;
   f->tool_bar_redisplayed = false;
   f->tool_bar_resized = false;
   f->column_width = 1;  /* !FRAME_WINDOW_P value.  */
@@ -856,6 +870,7 @@ make_frame (bool mini_p)
   f->no_accept_focus = false;
   f->z_group = z_group_none;
   f->tooltip = false;
+  f->last_tab_bar_item = -1;
 #ifndef HAVE_EXT_TOOL_BAR
   f->last_tool_bar_item = -1;
 #endif
@@ -3390,6 +3405,23 @@ to `frame-height'). */)
     return make_fixnum (FRAME_TOTAL_LINES (f));
 }
 
+DEFUN ("tab-bar-pixel-width", Ftab_bar_pixel_width,
+       Stab_bar_pixel_width, 0, 1, 0,
+       doc: /* Return width in pixels of FRAME's tab bar.
+The result is greater than zero only when the tab bar is on the left
+or right side of FRAME.  If FRAME is omitted or nil, the selected frame
+is used.  */)
+  (Lisp_Object frame)
+{
+#ifdef FRAME_TABBAR_WIDTH
+  struct frame *f = decode_any_frame (frame);
+
+  if (FRAME_WINDOW_P (f))
+    return make_fixnum (FRAME_TABBAR_WIDTH (f));
+#endif
+  return make_fixnum (0);
+}
+
 DEFUN ("tool-bar-pixel-width", Ftool_bar_pixel_width,
        Stool_bar_pixel_width, 0, 1, 0,
        doc: /* Return width in pixels of FRAME's tool bar.
@@ -3695,6 +3727,7 @@ static const struct frame_parm_table frame_parms[] =
   {"vertical-scroll-bars",     SYMBOL_INDEX (Qvertical_scroll_bars)},
   {"horizontal-scroll-bars",   SYMBOL_INDEX (Qhorizontal_scroll_bars)},
   {"visibility",               SYMBOL_INDEX (Qvisibility)},
+  {"tab-bar-lines",            SYMBOL_INDEX (Qtab_bar_lines)},
   {"tool-bar-lines",           SYMBOL_INDEX (Qtool_bar_lines)},
   {"scroll-bar-foreground",    SYMBOL_INDEX (Qscroll_bar_foreground)},
   {"scroll-bar-background",    SYMBOL_INDEX (Qscroll_bar_background)},
@@ -4450,6 +4483,8 @@ gui_set_font (struct frame *f, Lisp_Object arg, 
Lisp_Object oldval)
 #ifdef HAVE_X_WINDOWS
   store_frame_param (f, Qfont_parameter, font_param);
 #endif
+  /* Recalculate tabbar height.  */
+  f->n_tab_bar_rows = 0;
   /* Recalculate toolbar height.  */
   f->n_tool_bar_rows = 0;
 
@@ -5390,7 +5425,7 @@ On Nextstep, this just calls `ns-parse-geometry'.  */)
 #define DEFAULT_COLS 80
 
 long
-gui_figure_window_size (struct frame *f, Lisp_Object parms, bool toolbar_p,
+gui_figure_window_size (struct frame *f, Lisp_Object parms, bool tabbar_p, 
bool toolbar_p,
                         int *x_width, int *x_height)
 {
   Lisp_Object height, width, user_size, top, left, user_position;
@@ -5411,6 +5446,36 @@ gui_figure_window_size (struct frame *f, Lisp_Object 
parms, bool toolbar_p,
   f->top_pos = 0;
   f->left_pos = 0;
 
+  /* Calculate a tab bar height so that the user gets a text display
+     area of the size he specified with -g or via .Xdefaults.  Later
+     changes of the tab bar height don't change the frame size.  This
+     is done so that users can create tall Emacs frames without having
+     to guess how tall the tab bar will get.  */
+  if (tabbar_p && FRAME_TAB_BAR_LINES (f))
+    {
+      if (frame_default_tab_bar_height)
+       FRAME_TAB_BAR_HEIGHT (f) = frame_default_tab_bar_height;
+      else
+       {
+         int margin, relief;
+
+         relief = (tab_bar_button_relief < 0
+                   ? DEFAULT_TAB_BAR_BUTTON_RELIEF
+                   : min (tab_bar_button_relief, 1000000));
+
+         if (RANGED_FIXNUMP (1, Vtab_bar_button_margin, INT_MAX))
+           margin = XFIXNAT (Vtab_bar_button_margin);
+         else if (CONSP (Vtab_bar_button_margin)
+                  && RANGED_FIXNUMP (1, XCDR (Vtab_bar_button_margin), 
INT_MAX))
+           margin = XFIXNAT (XCDR (Vtab_bar_button_margin));
+         else
+           margin = 0;
+
+         FRAME_TAB_BAR_HEIGHT (f)
+           = DEFAULT_TAB_BAR_IMAGE_HEIGHT + 2 * margin + 2 * relief;
+       }
+    }
+
   /* Calculate a tool bar height so that the user gets a text display
      area of the size he specified with -g or via .Xdefaults.  Later
      changes of the tool bar height don't change the frame size.  This
@@ -5837,6 +5902,7 @@ syms_of_frame (void)
   DEFSYM (Qtitle_bar_size, "title-bar-size");
   DEFSYM (Qmenu_bar_external, "menu-bar-external");
   DEFSYM (Qmenu_bar_size, "menu-bar-size");
+  DEFSYM (Qtab_bar_size, "tab-bar-size");
   DEFSYM (Qtool_bar_external, "tool-bar-external");
   DEFSYM (Qtool_bar_size, "tool-bar-size");
   /* The following are used for frame_size_history.  */
@@ -5860,7 +5926,9 @@ syms_of_frame (void)
   DEFSYM (Qx_net_wm_state, "x-net-wm-state");
   DEFSYM (Qx_handle_net_wm_state, "x-handle-net-wm-state");
   DEFSYM (Qtb_size_cb, "tb-size-cb");
+  DEFSYM (Qupdate_frame_tab_bar, "update-frame-tab-bar");
   DEFSYM (Qupdate_frame_tool_bar, "update-frame-tool-bar");
+  DEFSYM (Qfree_frame_tab_bar, "free-frame-tab-bar");
   DEFSYM (Qfree_frame_tool_bar, "free-frame-tool-bar");
   DEFSYM (Qx_set_menu_bar_lines, "x-set-menu-bar-lines");
   DEFSYM (Qchange_frame_size, "change-frame-size");
@@ -5910,6 +5978,7 @@ syms_of_frame (void)
   DEFSYM (Qscroll_bar_width, "scroll-bar-width");
   DEFSYM (Qsticky, "sticky");
   DEFSYM (Qtitle, "title");
+  DEFSYM (Qtab_bar_lines, "tab-bar-lines");
   DEFSYM (Qtool_bar_lines, "tool-bar-lines");
   DEFSYM (Qtool_bar_position, "tool-bar-position");
   DEFSYM (Qunsplittable, "unsplittable");
@@ -6071,6 +6140,14 @@ either customize it (see the info node `Easy 
Customization')
 or call the function `menu-bar-mode'.  */);
   Vmenu_bar_mode = Qt;
 
+  DEFVAR_LISP ("tab-bar-mode", Vtab_bar_mode,
+               doc: /* Non-nil if Tab-Bar mode is enabled.
+See the command `tab-bar-mode' for a description of this minor mode.
+Setting this variable directly does not take effect;
+either customize it (see the info node `Easy Customization')
+or call the function `tab-bar-mode'.  */);
+  Vtab_bar_mode = Qnil;
+
   DEFVAR_LISP ("tool-bar-mode", Vtool_bar_mode,
                doc: /* Non-nil if Tool-Bar mode is enabled.
 See the command `tool-bar-mode' for a description of this minor mode.
@@ -6200,7 +6277,7 @@ any of the parameters listed above, Emacs may try to 
enlarge the frame
 even if this option is non-nil.  */);
 #if defined (HAVE_WINDOW_SYSTEM)
 #if defined (USE_LUCID) || defined (USE_MOTIF) || defined (HAVE_NTGUI)
-  frame_inhibit_implied_resize = list1 (Qtool_bar_lines);
+  frame_inhibit_implied_resize = list2 (Qtab_bar_lines, Qtool_bar_lines);
 #else
   frame_inhibit_implied_resize = Qnil;
 #endif
@@ -6309,6 +6386,7 @@ iconify the top level frame instead.  */);
   defsubr (&Sframe_internal_border_width);
   defsubr (&Sright_divider_width);
   defsubr (&Sbottom_divider_width);
+  defsubr (&Stab_bar_pixel_width);
   defsubr (&Stool_bar_pixel_width);
   defsubr (&Sset_frame_height);
   defsubr (&Sset_frame_width);
diff --git a/src/frame.h b/src/frame.h
index fa45a32..1b21cc6 100644
--- a/src/frame.h
+++ b/src/frame.h
@@ -181,6 +181,15 @@ struct frame
   Lisp_Object menu_bar_window;
 #endif
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  /* A window used to display the tab-bar of a frame.  */
+  Lisp_Object tab_bar_window;
+
+  /* Desired and current contents displayed in that window.  */
+  Lisp_Object desired_tab_bar_string;
+  Lisp_Object current_tab_bar_string;
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   /* A window used to display the tool-bar of a frame.  */
   Lisp_Object tool_bar_window;
@@ -201,6 +210,9 @@ struct frame
   Lisp_Object font_data;
 #endif
 
+  /* Desired and current tab-bar items.  */
+  Lisp_Object tab_bar_items;
+
   /* Desired and current tool-bar items.  */
   Lisp_Object tool_bar_items;
   /* tool_bar_items should be the last Lisp_Object member.  */
@@ -208,6 +220,11 @@ struct frame
   /* Cache of realized faces.  */
   struct face_cache *face_cache;
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  /* Tab-bar item index of the item on which a mouse button was pressed.  */
+  int last_tab_bar_item;
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   /* Tool-bar item index of the item on which a mouse button was pressed.  */
   int last_tool_bar_item;
@@ -256,6 +273,12 @@ struct frame
   /* Set to true when current redisplay has updated frame.  */
   bool_bf updated_p : 1;
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  /* Set to true to minimize tab-bar height even when
+     auto-resize-tab-bar is set to grow-only.  */
+  bool_bf minimize_tab_bar_window_p : 1;
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   /* Set to true to minimize tool-bar height even when
      auto-resize-tool-bar is set to grow-only.  */
@@ -404,6 +427,10 @@ struct frame
   /* Set to true after this frame was made by `make-frame'.  */
   bool_bf after_make_frame : 1;
 
+  /* Whether the tab bar height change should be taken into account.  */
+  bool_bf tab_bar_redisplayed : 1;
+  bool_bf tab_bar_resized : 1;
+
   /* Whether the tool bar height change should be taken into account.  */
   bool_bf tool_bar_redisplayed : 1;
   bool_bf tool_bar_resized : 1;
@@ -435,6 +462,15 @@ struct frame
      last time run_window_change_functions was called on it.  */
   ptrdiff_t number_of_windows;
 
+  /* Number of lines (rounded up) of tab bar.  REMOVE THIS  */
+  int tab_bar_lines;
+
+  /* Height of frame internal tab bar in pixels.  */
+  int tab_bar_height;
+
+  int n_tab_bar_rows;
+  int n_tab_bar_items;
+
   /* Number of lines (rounded up) of tool bar.  REMOVE THIS  */
   int tool_bar_lines;
 
@@ -701,6 +737,28 @@ fset_title (struct frame *f, Lisp_Object val)
   f->title = val;
 }
 INLINE void
+fset_tab_bar_items (struct frame *f, Lisp_Object val)
+{
+  f->tab_bar_items = val;
+}
+#if defined (HAVE_WINDOW_SYSTEM)
+INLINE void
+fset_tab_bar_window (struct frame *f, Lisp_Object val)
+{
+  f->tab_bar_window = val;
+}
+INLINE void
+fset_current_tab_bar_string (struct frame *f, Lisp_Object val)
+{
+  f->current_tab_bar_string = val;
+}
+INLINE void
+fset_desired_tab_bar_string (struct frame *f, Lisp_Object val)
+{
+  f->desired_tab_bar_string = val;
+}
+#endif /* HAVE_WINDOW_SYSTEM */
+INLINE void
 fset_tool_bar_items (struct frame *f, Lisp_Object val)
 {
   f->tool_bar_items = val;
@@ -878,6 +936,12 @@ default_pixels_per_inch_y (void)
 /* Pixel height of frame F's menu bar.  */
 #define FRAME_MENU_BAR_HEIGHT(f) (f)->menu_bar_height
 
+/* Number of lines of frame F used for the tab-bar.  */
+#define FRAME_TAB_BAR_LINES(f) (f)->tab_bar_lines
+
+/* Pixel height of frame F's tab-bar.  */
+#define FRAME_TAB_BAR_HEIGHT(f) (f)->tab_bar_height
+
 /* True if this frame should display a tool bar
    in a way that does not use any text lines.  */
 #ifdef HAVE_EXT_TOOL_BAR
@@ -901,11 +965,11 @@ default_pixels_per_inch_y (void)
 
 /* Lines above the top-most window in frame F.  */
 #define FRAME_TOP_MARGIN(F) \
-  (FRAME_MENU_BAR_LINES (F) + FRAME_TOOL_BAR_LINES (F))
+  (FRAME_MENU_BAR_LINES (F) + FRAME_TAB_BAR_LINES (F) + FRAME_TOOL_BAR_LINES 
(F))
 
 /* Pixel height of frame F's top margin.  */
 #define FRAME_TOP_MARGIN_HEIGHT(F)                             \
-  (FRAME_MENU_BAR_HEIGHT (F) + FRAME_TOOL_BAR_HEIGHT (F))
+  (FRAME_MENU_BAR_HEIGHT (F) + FRAME_TAB_BAR_HEIGHT (F) + 
FRAME_TOOL_BAR_HEIGHT (F))
 
 /* True if this frame should display a menu bar
    in a way that does not use any text lines.  */
@@ -1255,6 +1319,8 @@ SET_FRAME_VISIBLE (struct frame *f, int v)
 extern Lisp_Object selected_frame;
 extern Lisp_Object old_selected_frame;
 
+extern int frame_default_tab_bar_height;
+
 #ifndef HAVE_EXT_TOOL_BAR
 extern int frame_default_tool_bar_height;
 #endif
@@ -1566,7 +1632,7 @@ extern void gui_set_horizontal_scroll_bars (struct frame 
*, Lisp_Object, Lisp_Ob
 extern void gui_set_scroll_bar_width (struct frame *, Lisp_Object, 
Lisp_Object);
 extern void gui_set_scroll_bar_height (struct frame *, Lisp_Object, 
Lisp_Object);
 
-extern long gui_figure_window_size (struct frame *, Lisp_Object, bool, int *, 
int *);
+extern long gui_figure_window_size (struct frame *, Lisp_Object, bool, bool, 
int *, int *);
 
 extern void gui_set_alpha (struct frame *, Lisp_Object, Lisp_Object);
 extern void gui_set_no_special_glyphs (struct frame *, Lisp_Object, 
Lisp_Object);
diff --git a/src/fringe.c b/src/fringe.c
index 4c5a4d7..2735ae7 100644
--- a/src/fringe.c
+++ b/src/fringe.c
@@ -634,7 +634,7 @@ draw_fringe_bitmap_1 (struct window *w, struct glyph_row 
*row, int left_p, int o
   /* Clear left fringe if no bitmap to draw or if bitmap doesn't fill
      the fringe.  */
   p.bx = -1;
-  header_line_height = WINDOW_HEADER_LINE_HEIGHT (w);
+  header_line_height = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT 
(w);
   p.by = WINDOW_TO_FRAME_PIXEL_Y (w, max (header_line_height, row->y));
   p.ny = row->visible_height;
   if (left_p)
@@ -1091,7 +1091,7 @@ update_window_fringes (struct window *w, bool 
keep_current_p)
              struct glyph_row *row1;
              int top_ind_max_y;
 
-             top_ind_min_y = WINDOW_HEADER_LINE_HEIGHT (w);
+             top_ind_min_y = WINDOW_TAB_LINE_HEIGHT (w) + 
WINDOW_HEADER_LINE_HEIGHT (w);
              top_ind_max_y = top_ind_min_y + fb->height;
              if (top_ind_max_y > yb)
                top_ind_max_y = yb;
@@ -1148,8 +1148,8 @@ update_window_fringes (struct window *w, bool 
keep_current_p)
 
              bot_ind_max_y = row->y + row->visible_height;
              bot_ind_min_y = bot_ind_max_y - fb->height;
-             if (bot_ind_min_y < WINDOW_HEADER_LINE_HEIGHT (w))
-               bot_ind_min_y = WINDOW_HEADER_LINE_HEIGHT (w);
+             if (bot_ind_min_y < WINDOW_TAB_LINE_HEIGHT (w) + 
WINDOW_HEADER_LINE_HEIGHT (w))
+               bot_ind_min_y = WINDOW_TAB_LINE_HEIGHT (w) + 
WINDOW_HEADER_LINE_HEIGHT (w);
 
              for (y = row->y, rn = bot_ind_rn - 1;
                   y >= bot_ind_min_y && rn >= 0;
diff --git a/src/gtkutil.c b/src/gtkutil.c
index 16d7655..8a2fc3a 100644
--- a/src/gtkutil.c
+++ b/src/gtkutil.c
@@ -951,8 +951,8 @@ xg_frame_set_char_size (struct frame *f, int width, int 
height)
   Lisp_Object fullscreen = get_frame_param (f, Qfullscreen);
   gint gwidth, gheight;
   int totalheight
-    = pixelheight + FRAME_TOOLBAR_HEIGHT (f) + FRAME_MENUBAR_HEIGHT (f);
-  int totalwidth = pixelwidth + FRAME_TOOLBAR_WIDTH (f);
+    = pixelheight + FRAME_TOOLBAR_HEIGHT (f) + FRAME_TABBAR_HEIGHT (f) + 
FRAME_MENUBAR_HEIGHT (f);
+  int totalwidth = pixelwidth + FRAME_TABBAR_WIDTH (f) + FRAME_TOOLBAR_WIDTH 
(f);
 
   if (FRAME_PIXEL_HEIGHT (f) == 0)
     return;
@@ -1437,9 +1437,9 @@ x_wm_set_size_hint (struct frame *f, long int flags, bool 
user_position)
   /* Use one row/col here so base_height/width does not become zero.
      Gtk+ and/or Unity on Ubuntu 12.04 can't handle it.
      Obviously this makes the row/col value displayed off by 1.  */
-  base_width = FRAME_TEXT_COLS_TO_PIXEL_WIDTH (f, 1) + FRAME_TOOLBAR_WIDTH (f);
+  base_width = FRAME_TEXT_COLS_TO_PIXEL_WIDTH (f, 1) + FRAME_TABBAR_WIDTH (f) 
+ FRAME_TOOLBAR_WIDTH (f);
   base_height = FRAME_TEXT_LINES_TO_PIXEL_HEIGHT (f, 1)
-    + FRAME_MENUBAR_HEIGHT (f) + FRAME_TOOLBAR_HEIGHT (f);
+    + FRAME_MENUBAR_HEIGHT (f) + FRAME_TABBAR_HEIGHT (f) + 
FRAME_TOOLBAR_HEIGHT (f);
 
   size_hints.base_width = base_width;
   size_hints.base_height = base_height;
diff --git a/src/keyboard.c b/src/keyboard.c
index 1b9a603..44f6421 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -2385,7 +2385,7 @@ read_char (int commandflag, Lisp_Object map,
       if (used_mouse_menu
          /* Also check was_disabled so last-nonmenu-event won't return
             a bad value when submenus are involved.  (Bug#447)  */
-         && (EQ (c, Qtool_bar) || EQ (c, Qmenu_bar) || was_disabled))
+         && (EQ (c, Qtool_bar) || EQ (c, Qtab_bar) || EQ (c, Qmenu_bar) || 
was_disabled))
        *used_mouse_menu = true;
 
       goto reread_for_input_method;
@@ -2666,6 +2666,7 @@ read_char (int commandflag, Lisp_Object map,
       && !NILP (prev_event)
       && EVENT_HAS_PARAMETERS (prev_event)
       && !EQ (XCAR (prev_event), Qmenu_bar)
+      && !EQ (XCAR (prev_event), Qtab_bar)
       && !EQ (XCAR (prev_event), Qtool_bar)
       /* Don't bring up a menu if we already have another event.  */
       && !CONSP (Vunread_command_events))
@@ -2930,7 +2931,7 @@ read_char (int commandflag, Lisp_Object map,
       posn = POSN_POSN (xevent_start (c));
       /* Handle menu-bar events:
         insert the dummy prefix event `menu-bar'.  */
-      if (EQ (posn, Qmenu_bar) || EQ (posn, Qtool_bar))
+      if (EQ (posn, Qmenu_bar) || EQ (posn, Qtab_bar) || EQ (posn, Qtool_bar))
        {
          /* Change menu-bar to (menu-bar) as the event "position".  */
          POSN_SET_POSN (xevent_start (c), list1 (posn));
@@ -3974,6 +3975,7 @@ kbd_buffer_get_event (KBOARD **kbp,
              if (used_mouse_menu
                  && !EQ (event->ie.frame_or_window, event->ie.arg)
                  && (event->kind == MENU_BAR_EVENT
+                     || event->kind == TAB_BAR_EVENT
                      || event->kind == TOOL_BAR_EVENT))
                *used_mouse_menu = true;
 #endif
@@ -5012,7 +5014,7 @@ make_lispy_position (struct frame *f, Lisp_Object x, 
Lisp_Object y,
   int xret = 0, yret = 0;
   /* The window or frame under frame pixel coordinates (x,y)  */
   Lisp_Object window_or_frame = f
-    ? window_from_coordinates (f, XFIXNUM (x), XFIXNUM (y), &part, 0)
+    ? window_from_coordinates (f, XFIXNUM (x), XFIXNUM (y), &part, 0, 0)
     : Qnil;
 
   if (WINDOWP (window_or_frame))
@@ -5036,17 +5038,20 @@ make_lispy_position (struct frame *f, Lisp_Object x, 
Lisp_Object y,
       if (part == ON_TEXT)
        {
          xret = XFIXNUM (x) - window_box_left (w, TEXT_AREA);
-         yret = wy - WINDOW_HEADER_LINE_HEIGHT (w);
+         yret = wy - WINDOW_TAB_LINE_HEIGHT (w) - WINDOW_HEADER_LINE_HEIGHT 
(w);
        }
       /* For mode line and header line clicks, return X, Y relative to
         the left window edge.  Use mode_line_string to look for a
         string on the click position.  */
-      else if (part == ON_MODE_LINE || part == ON_HEADER_LINE)
+      else if (part == ON_MODE_LINE || part == ON_TAB_LINE || part == 
ON_HEADER_LINE)
        {
          Lisp_Object string;
          ptrdiff_t charpos;
 
-         posn = (part == ON_MODE_LINE) ? Qmode_line : Qheader_line;
+         posn = (part == ON_MODE_LINE ? Qmode_line
+                  : (part == ON_TAB_LINE ? Qtab_line
+                     : Qheader_line));
+
          /* Note that mode_line_string takes COL, ROW as pixels and
             converts them to characters.  */
          col = wx;
@@ -5075,7 +5080,7 @@ make_lispy_position (struct frame *f, Lisp_Object x, 
Lisp_Object y,
          if (STRINGP (string))
            string_info = Fcons (string, make_fixnum (charpos));
          xret = wx;
-         yret = wy - WINDOW_HEADER_LINE_HEIGHT (w);
+         yret = wy - WINDOW_TAB_LINE_HEIGHT (w) - WINDOW_HEADER_LINE_HEIGHT 
(w);
        }
       else if (part == ON_LEFT_FRINGE)
        {
@@ -5085,7 +5090,7 @@ make_lispy_position (struct frame *f, Lisp_Object x, 
Lisp_Object y,
          dx = wx
            - (WINDOW_HAS_FRINGES_OUTSIDE_MARGINS (w)
               ? 0 : window_box_width (w, LEFT_MARGIN_AREA));
-         dy = yret = wy - WINDOW_HEADER_LINE_HEIGHT (w);
+         dy = yret = wy - WINDOW_TAB_LINE_HEIGHT (w) - 
WINDOW_HEADER_LINE_HEIGHT (w);
        }
       else if (part == ON_RIGHT_FRINGE)
        {
@@ -5098,7 +5103,7 @@ make_lispy_position (struct frame *f, Lisp_Object x, 
Lisp_Object y,
            - (WINDOW_HAS_FRINGES_OUTSIDE_MARGINS (w)
               ? window_box_width (w, RIGHT_MARGIN_AREA)
               : 0);
-         dy = yret = wy - WINDOW_HEADER_LINE_HEIGHT (w);
+         dy = yret = wy - WINDOW_TAB_LINE_HEIGHT (w) - 
WINDOW_HEADER_LINE_HEIGHT (w);
        }
       else if (part == ON_VERTICAL_BORDER)
        {
@@ -5953,6 +5958,16 @@ make_lispy_event (struct input_event *event)
       /* Make an event (select-window (WINDOW)).  */
       return list2 (Qselect_window, list1 (event->frame_or_window));
 
+    case TAB_BAR_EVENT:
+      if (EQ (event->arg, event->frame_or_window))
+       /* This is the prefix key.  We translate this to
+          `(tab_bar)' because the code in keyboard.c for tab bar
+          events, which we use, relies on this.  */
+       return list1 (Qtab_bar);
+      else if (SYMBOLP (event->arg))
+       return apply_modifiers (event->modifiers, event->arg);
+      return event->arg;
+
     case TOOL_BAR_EVENT:
       if (EQ (event->arg, event->frame_or_window))
        /* This is the prefix key.  We translate this to
@@ -6730,6 +6745,7 @@ lucid_event_type_list_p (Lisp_Object object)
   if (EQ (XCAR (object), Qhelp_echo)
       || EQ (XCAR (object), Qvertical_line)
       || EQ (XCAR (object), Qmode_line)
+      || EQ (XCAR (object), Qtab_line)
       || EQ (XCAR (object), Qheader_line))
     return 0;
 
@@ -7891,6 +7907,463 @@ parse_menu_item (Lisp_Object item, int inmenubar)
 
 
 /***********************************************************************
+                              Tab-bars
+ ***********************************************************************/
+
+/* A vector holding tab bar items while they are parsed in function
+   tab_bar_items. Each item occupies TAB_BAR_ITEM_NSCLOTS elements
+   in the vector.  */
+
+static Lisp_Object tab_bar_items_vector;
+
+/* A vector holding the result of parse_tab_bar_item.  Layout is like
+   the one for a single item in tab_bar_items_vector.  */
+
+static Lisp_Object tab_bar_item_properties;
+
+/* Next free index in tab_bar_items_vector.  */
+
+static int ntab_bar_items;
+
+/* Function prototypes.  */
+
+static void init_tab_bar_items (Lisp_Object);
+static void process_tab_bar_item (Lisp_Object, Lisp_Object, Lisp_Object,
+                                  void *);
+static bool parse_tab_bar_item (Lisp_Object, Lisp_Object);
+static void append_tab_bar_item (void);
+
+
+/* Return a vector of tab bar items for keymaps currently in effect.
+   Reuse vector REUSE if non-nil.  Return in *NITEMS the number of
+   tab bar items found.  */
+
+Lisp_Object
+tab_bar_items (Lisp_Object reuse, int *nitems)
+{
+  Lisp_Object *maps;
+  Lisp_Object mapsbuf[3];
+  ptrdiff_t nmaps, i;
+  Lisp_Object oquit;
+  Lisp_Object *tmaps;
+  USE_SAFE_ALLOCA;
+
+  *nitems = 0;
+
+  /* In order to build the menus, we need to call the keymap
+     accessors.  They all call maybe_quit.  But this function is called
+     during redisplay, during which a quit is fatal.  So inhibit
+     quitting while building the menus.  We do this instead of
+     specbind because (1) errors will clear it anyway and (2) this
+     avoids risk of specpdl overflow.  */
+  oquit = Vinhibit_quit;
+  Vinhibit_quit = Qt;
+
+  /* Initialize tab_bar_items_vector and protect it from GC.  */
+  init_tab_bar_items (reuse);
+
+  /* Build list of keymaps in maps.  Set nmaps to the number of maps
+     to process.  */
+
+  /* Should overriding-terminal-local-map and overriding-local-map apply?  */
+  if (!NILP (Voverriding_local_map_menu_flag)
+      && !NILP (Voverriding_local_map))
+    {
+      /* Yes, use them (if non-nil) as well as the global map.  */
+      maps = mapsbuf;
+      nmaps = 0;
+      if (!NILP (KVAR (current_kboard, Voverriding_terminal_local_map)))
+       maps[nmaps++] = KVAR (current_kboard, Voverriding_terminal_local_map);
+      if (!NILP (Voverriding_local_map))
+       maps[nmaps++] = Voverriding_local_map;
+    }
+  else
+    {
+      /* No, so use major and minor mode keymaps and keymap property.
+        Note that tab-bar bindings in the local-map and keymap
+        properties may not work reliably, as they are only
+        recognized when the tab-bar (or mode-line) is updated,
+        which does not normally happen after every command.  */
+      ptrdiff_t nminor = current_minor_maps (NULL, &tmaps);
+      SAFE_NALLOCA (maps, 1, nminor + 4);
+      nmaps = 0;
+      Lisp_Object tem = KVAR (current_kboard, Voverriding_terminal_local_map);
+      if (!NILP (tem) && !NILP (Voverriding_local_map_menu_flag))
+       maps[nmaps++] = tem;
+      if (tem = get_local_map (PT, current_buffer, Qkeymap), !NILP (tem))
+       maps[nmaps++] = tem;
+      if (nminor != 0)
+       {
+         memcpy (maps + nmaps, tmaps, nminor * sizeof (maps[0]));
+         nmaps += nminor;
+       }
+      maps[nmaps++] = get_local_map (PT, current_buffer, Qlocal_map);
+    }
+
+  /* Add global keymap at the end.  */
+  maps[nmaps++] = current_global_map;
+
+  /* Process maps in reverse order and look up in each map the prefix
+     key `tab-bar'.  */
+  for (i = nmaps - 1; i >= 0; --i)
+    if (!NILP (maps[i]))
+      {
+       Lisp_Object keymap;
+
+       keymap = get_keymap (access_keymap (maps[i], Qtab_bar, 1, 0, 1), 0, 1);
+       if (CONSP (keymap))
+         map_keymap (keymap, process_tab_bar_item, Qnil, NULL, 1);
+      }
+
+  Vinhibit_quit = oquit;
+  *nitems = ntab_bar_items / TAB_BAR_ITEM_NSLOTS;
+  SAFE_FREE ();
+  return tab_bar_items_vector;
+}
+
+
+/* Process the definition of KEY which is DEF.  */
+
+static void
+process_tab_bar_item (Lisp_Object key, Lisp_Object def, Lisp_Object data, void 
*args)
+{
+  int i;
+
+  if (EQ (def, Qundefined))
+    {
+      /* If a map has an explicit `undefined' as definition,
+        discard any previously made item.  */
+      for (i = 0; i < ntab_bar_items; i += TAB_BAR_ITEM_NSLOTS)
+       {
+         Lisp_Object *v = XVECTOR (tab_bar_items_vector)->contents + i;
+
+         if (EQ (key, v[TAB_BAR_ITEM_KEY]))
+           {
+             if (ntab_bar_items > i + TAB_BAR_ITEM_NSLOTS)
+               memmove (v, v + TAB_BAR_ITEM_NSLOTS,
+                        ((ntab_bar_items - i - TAB_BAR_ITEM_NSLOTS)
+                         * word_size));
+             ntab_bar_items -= TAB_BAR_ITEM_NSLOTS;
+             break;
+           }
+       }
+    }
+  else if (parse_tab_bar_item (key, def))
+    /* Append a new tab bar item to tab_bar_items_vector.  Accept
+       more than one definition for the same key.  */
+    append_tab_bar_item ();
+}
+
+/* Access slot with index IDX of vector tab_bar_item_properties.  */
+#define PROP(IDX) AREF (tab_bar_item_properties, (IDX))
+static void
+set_prop_tab_bar (ptrdiff_t idx, Lisp_Object val)
+{
+  ASET (tab_bar_item_properties, idx, val);
+}
+
+
+/* Parse a tab bar item specification ITEM for key KEY and return the
+   result in tab_bar_item_properties.  Value is false if ITEM is
+   invalid.
+
+   ITEM is a list `(menu-item CAPTION BINDING PROPS...)'.
+
+   CAPTION is the caption of the item,  If it's not a string, it is
+   evaluated to get a string.
+
+   BINDING is the tab bar item's binding.  Tab-bar items with keymaps
+   as binding are currently ignored.
+
+   The following properties are recognized:
+
+   - `:enable FORM'.
+
+   FORM is evaluated and specifies whether the tab bar item is
+   enabled or disabled.
+
+   - `:visible FORM'
+
+   FORM is evaluated and specifies whether the tab bar item is visible.
+
+   - `:filter FUNCTION'
+
+   FUNCTION is invoked with one parameter `(quote BINDING)'.  Its
+   result is stored as the new binding.
+
+   - `:button (TYPE SELECTED)'
+
+   TYPE must be one of `:radio' or `:toggle'.  SELECTED is evaluated
+   and specifies whether the button is selected (pressed) or not.
+
+   - `:image IMAGES'
+
+   IMAGES is either a single image specification or a vector of four
+   image specifications.  See enum tab_bar_item_images.
+
+   - `:help HELP-STRING'.
+
+   Gives a help string to display for the tab bar item.
+
+   - `:label LABEL-STRING'.
+
+   A text label to show with the tab bar button if labels are enabled.  */
+
+static bool
+parse_tab_bar_item (Lisp_Object key, Lisp_Object item)
+{
+  Lisp_Object filter = Qnil;
+  Lisp_Object caption;
+  int i;
+  bool have_label = false;
+
+  /* Definition looks like `(menu-item CAPTION BINDING PROPS...)'.
+     Rule out items that aren't lists, don't start with
+     `menu-item' or whose rest following `tab-bar-item' is not a
+     list.  */
+  if (!CONSP (item))
+    return 0;
+
+  /* As an exception, allow old-style menu separators.  */
+  if (STRINGP (XCAR (item)))
+    item = list1 (XCAR (item));
+  else if (!EQ (XCAR (item), Qmenu_item)
+          || (item = XCDR (item), !CONSP (item)))
+    return 0;
+
+  /* Create tab_bar_item_properties vector if necessary.  Reset it to
+     defaults.  */
+  if (VECTORP (tab_bar_item_properties))
+    {
+      for (i = 0; i < TAB_BAR_ITEM_NSLOTS; ++i)
+       set_prop_tab_bar (i, Qnil);
+    }
+  else
+    tab_bar_item_properties = make_nil_vector (TAB_BAR_ITEM_NSLOTS);
+
+  /* Set defaults.  */
+  set_prop_tab_bar (TAB_BAR_ITEM_KEY, key);
+  set_prop_tab_bar (TAB_BAR_ITEM_ENABLED_P, Qt);
+
+  /* Get the caption of the item.  If the caption is not a string,
+     evaluate it to get a string.  If we don't get a string, skip this
+     item.  */
+  caption = XCAR (item);
+  if (!STRINGP (caption))
+    {
+      caption = menu_item_eval_property (caption);
+      if (!STRINGP (caption))
+       return 0;
+    }
+  set_prop_tab_bar (TAB_BAR_ITEM_CAPTION, caption);
+
+  /* If the rest following the caption is not a list, the menu item is
+     either a separator, or invalid.  */
+  item = XCDR (item);
+  if (!CONSP (item))
+    {
+      if (menu_separator_name_p (SSDATA (caption)))
+       {
+         set_prop_tab_bar (TAB_BAR_ITEM_TYPE, Qt);
+         /* If we use build_desired_tab_bar_string to render the
+            tab bar, the separator is rendered as an image.  */
+         set_prop_tab_bar (TAB_BAR_ITEM_IMAGES,
+                   (menu_item_eval_property
+                    (Vtab_bar_separator_image_expression)));
+         set_prop_tab_bar (TAB_BAR_ITEM_ENABLED_P, Qnil);
+         set_prop_tab_bar (TAB_BAR_ITEM_SELECTED_P, Qnil);
+         set_prop_tab_bar (TAB_BAR_ITEM_CAPTION, Qnil);
+         return 1;
+       }
+      return 0;
+    }
+
+  /* Store the binding.  */
+  set_prop_tab_bar (TAB_BAR_ITEM_BINDING, XCAR (item));
+  item = XCDR (item);
+
+  /* Ignore cached key binding, if any.  */
+  if (CONSP (item) && CONSP (XCAR (item)))
+    item = XCDR (item);
+
+  /* Process the rest of the properties.  */
+  for (; CONSP (item) && CONSP (XCDR (item)); item = XCDR (XCDR (item)))
+    {
+      Lisp_Object ikey, value;
+
+      ikey = XCAR (item);
+      value = XCAR (XCDR (item));
+
+      if (EQ (ikey, QCenable))
+       {
+         /* `:enable FORM'.  */
+         if (!NILP (Venable_disabled_menus_and_buttons))
+           set_prop_tab_bar (TAB_BAR_ITEM_ENABLED_P, Qt);
+         else
+           set_prop_tab_bar (TAB_BAR_ITEM_ENABLED_P, value);
+       }
+      else if (EQ (ikey, QCvisible))
+       {
+         /* `:visible FORM'.  If got a visible property and that
+            evaluates to nil then ignore this item.  */
+         if (NILP (menu_item_eval_property (value)))
+           return 0;
+       }
+      else if (EQ (ikey, QChelp))
+        /* `:help HELP-STRING'.  */
+        set_prop_tab_bar (TAB_BAR_ITEM_HELP, value);
+      else if (EQ (ikey, QCvert_only))
+        /* `:vert-only t/nil'.  */
+        set_prop_tab_bar (TAB_BAR_ITEM_VERT_ONLY, value);
+      else if (EQ (ikey, QClabel))
+        {
+          const char *bad_label = "!!?GARBLED ITEM?!!";
+          /* `:label LABEL-STRING'.  */
+          set_prop_tab_bar (TAB_BAR_ITEM_LABEL,
+                   STRINGP (value) ? value : build_string (bad_label));
+          have_label = true;
+        }
+      else if (EQ (ikey, QCfilter))
+       /* ':filter FORM'.  */
+       filter = value;
+      else if (EQ (ikey, QCbutton) && CONSP (value))
+       {
+         /* `:button (TYPE . SELECTED)'.  */
+         Lisp_Object type, selected;
+
+         type = XCAR (value);
+         selected = XCDR (value);
+         if (EQ (type, QCtoggle) || EQ (type, QCradio))
+           {
+             set_prop_tab_bar (TAB_BAR_ITEM_SELECTED_P, selected);
+             set_prop_tab_bar (TAB_BAR_ITEM_TYPE, type);
+           }
+       }
+      else if (EQ (ikey, QCimage)
+              && (CONSP (value)
+                  || (VECTORP (value) && ASIZE (value) == 4)))
+       /* Value is either a single image specification or a vector
+          of 4 such specifications for the different button states.  */
+       set_prop_tab_bar (TAB_BAR_ITEM_IMAGES, value);
+      else if (EQ (ikey, QCrtl))
+        /* ':rtl STRING' */
+       set_prop_tab_bar (TAB_BAR_ITEM_RTL_IMAGE, value);
+    }
+
+
+  if (!have_label)
+    {
+      /* Try to make one from caption and key.  */
+      Lisp_Object tkey = PROP (TAB_BAR_ITEM_KEY);
+      Lisp_Object tcapt = PROP (TAB_BAR_ITEM_CAPTION);
+      const char *label = SYMBOLP (tkey) ? SSDATA (SYMBOL_NAME (tkey)) : "";
+      const char *capt = STRINGP (tcapt) ? SSDATA (tcapt) : "";
+      ptrdiff_t max_lbl_size =
+       2 * max (0, min (tab_bar_max_label_size, STRING_BYTES_BOUND / 2)) + 1;
+      char *buf = xmalloc (max_lbl_size);
+      Lisp_Object new_lbl;
+      ptrdiff_t caption_len = strnlen (capt, max_lbl_size);
+
+      if (0 < caption_len && caption_len < max_lbl_size)
+        {
+          strcpy (buf, capt);
+          while (caption_len > 0 && buf[caption_len - 1] == '.')
+            caption_len--;
+         buf[caption_len] = '\0';
+         label = capt = buf;
+        }
+
+      ptrdiff_t label_len = strnlen (label, max_lbl_size);
+      if (0 < label_len && label_len < max_lbl_size)
+        {
+          ptrdiff_t j;
+          if (label != buf)
+           strcpy (buf, label);
+
+          for (j = 0; buf[j] != '\0'; ++j)
+           if (buf[j] == '-')
+             buf[j] = ' ';
+          label = buf;
+        }
+      else
+       label = "";
+
+      new_lbl = Fupcase_initials (build_string (label));
+      if (SCHARS (new_lbl) <= tab_bar_max_label_size)
+        set_prop_tab_bar (TAB_BAR_ITEM_LABEL, new_lbl);
+      else
+        set_prop_tab_bar (TAB_BAR_ITEM_LABEL, empty_unibyte_string);
+      xfree (buf);
+    }
+
+  /* If got a filter apply it on binding.  */
+  if (!NILP (filter))
+    set_prop_tab_bar (TAB_BAR_ITEM_BINDING,
+             (menu_item_eval_property
+              (list2 (filter,
+                      list2 (Qquote,
+                             PROP (TAB_BAR_ITEM_BINDING))))));
+
+  /* See if the binding is a keymap.  Give up if it is.  */
+  if (CONSP (get_keymap (PROP (TAB_BAR_ITEM_BINDING), 0, 1)))
+    return 0;
+
+  /* Enable or disable selection of item.  */
+  if (!EQ (PROP (TAB_BAR_ITEM_ENABLED_P), Qt))
+    set_prop_tab_bar (TAB_BAR_ITEM_ENABLED_P,
+             menu_item_eval_property (PROP (TAB_BAR_ITEM_ENABLED_P)));
+
+  /* Handle radio buttons or toggle boxes.  */
+  if (!NILP (PROP (TAB_BAR_ITEM_SELECTED_P)))
+    set_prop_tab_bar (TAB_BAR_ITEM_SELECTED_P,
+             menu_item_eval_property (PROP (TAB_BAR_ITEM_SELECTED_P)));
+
+  return 1;
+
+#undef PROP
+}
+
+
+/* Initialize tab_bar_items_vector.  REUSE, if non-nil, is a vector
+   that can be reused.  */
+
+static void
+init_tab_bar_items (Lisp_Object reuse)
+{
+  if (VECTORP (reuse))
+    tab_bar_items_vector = reuse;
+  else
+    tab_bar_items_vector = make_nil_vector (64);
+  ntab_bar_items = 0;
+}
+
+
+/* Append parsed tab bar item properties from
+   tab_bar_item_properties */
+
+static void
+append_tab_bar_item (void)
+{
+  ptrdiff_t incr
+    = (ntab_bar_items
+       - (ASIZE (tab_bar_items_vector) - TAB_BAR_ITEM_NSLOTS));
+
+  /* Enlarge tab_bar_items_vector if necessary.  */
+  if (incr > 0)
+    tab_bar_items_vector = larger_vector (tab_bar_items_vector, incr, -1);
+
+  /* Append entries from tab_bar_item_properties to the end of
+     tab_bar_items_vector.  */
+  vcopy (tab_bar_items_vector, ntab_bar_items,
+        XVECTOR (tab_bar_item_properties)->contents, TAB_BAR_ITEM_NSLOTS);
+  ntab_bar_items += TAB_BAR_ITEM_NSLOTS;
+}
+
+
+
+
+
+/***********************************************************************
                               Tool-bars
  ***********************************************************************/
 
@@ -8402,6 +8875,7 @@ read_char_x_menu_prompt (Lisp_Object map,
      use a real menu for mouse selection.  */
   if (EVENT_HAS_PARAMETERS (prev_event)
       && !EQ (XCAR (prev_event), Qmenu_bar)
+      && !EQ (XCAR (prev_event), Qtab_bar)
       && !EQ (XCAR (prev_event), Qtool_bar))
     {
       /* Display the menu and get the selection.  */
@@ -9377,7 +9851,7 @@ read_key_sequence (Lisp_Object *keybuf, Lisp_Object 
prompt,
              posn = POSN_POSN (xevent_start (key));
              /* Handle menu-bar events:
                 insert the dummy prefix event `menu-bar'.  */
-             if (EQ (posn, Qmenu_bar) || EQ (posn, Qtool_bar))
+             if (EQ (posn, Qmenu_bar) || EQ (posn, Qtab_bar) || EQ (posn, 
Qtool_bar))
                {
                  if (READ_KEY_ELTS - t <= 1)
                    error ("Key sequence too long");
@@ -11057,6 +11531,11 @@ syms_of_keyboard (void)
   staticpro (&item_properties);
   item_properties = Qnil;
 
+  staticpro (&tab_bar_item_properties);
+  tab_bar_item_properties = Qnil;
+  staticpro (&tab_bar_items_vector);
+  tab_bar_items_vector = Qnil;
+
   staticpro (&tool_bar_item_properties);
   tool_bar_item_properties = Qnil;
   staticpro (&tool_bar_items_vector);
@@ -11610,6 +12089,12 @@ See also `pre-command-hook'.  */);
 The elements of the list are event types that may have menu bar bindings.  */);
   Vmenu_bar_final_items = Qnil;
 
+  DEFVAR_LISP ("tab-bar-separator-image-expression", 
Vtab_bar_separator_image_expression,
+    doc: /* Expression evaluating to the image spec for a tab-bar separator.
+This is used internally by graphical displays that do not render
+tab-bar separators natively.  Otherwise it is unused (e.g. on GTK).  */);
+  Vtab_bar_separator_image_expression = Qnil;
+
   DEFVAR_LISP ("tool-bar-separator-image-expression", 
Vtool_bar_separator_image_expression,
     doc: /* Expression evaluating to the image spec for a tool-bar separator.
 This is used internally by graphical displays that do not render
diff --git a/src/keymap.c b/src/keymap.c
index b1e09a9..c92556b 100644
--- a/src/keymap.c
+++ b/src/keymap.c
@@ -3663,7 +3663,7 @@ be preferred.  */);
   DEFSYM (Qmode_line, "mode-line");
 
   staticpro (&Vmouse_events);
-  Vmouse_events = pure_list (Qmenu_bar, Qtool_bar, Qheader_line, Qmode_line,
+  Vmouse_events = pure_list (Qmenu_bar, Qtab_bar, Qtool_bar, Qtab_line, 
Qheader_line, Qmode_line,
                             intern_c_string ("mouse-1"),
                             intern_c_string ("mouse-2"),
                             intern_c_string ("mouse-3"),
diff --git a/src/lisp.h b/src/lisp.h
index a7b19ab..d571b96 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4388,6 +4388,7 @@ extern bool input_pending;
 extern sigjmp_buf return_to_command_loop;
 #endif
 extern Lisp_Object menu_bar_items (Lisp_Object);
+extern Lisp_Object tab_bar_items (Lisp_Object, int *);
 extern Lisp_Object tool_bar_items (Lisp_Object, int *);
 extern void discard_mouse_events (void);
 #ifdef USABLE_SIGIO
diff --git a/src/menu.c b/src/menu.c
index f67bdf0..3d9cdb0 100644
--- a/src/menu.c
+++ b/src/menu.c
@@ -1130,6 +1130,7 @@ x_popup_menu_1 (Lisp_Object position, Lisp_Object menu)
     /* Decode the first argument: find the window and the coordinates.  */
     if (EQ (position, Qt)
        || (CONSP (position) && (EQ (XCAR (position), Qmenu_bar)
+                                || EQ (XCAR (position), Qtab_bar)
                                 || EQ (XCAR (position), Qtool_bar))))
       {
        get_current_pos_p = 1;
@@ -1506,6 +1507,7 @@ for instance using the window manager, then this produces 
a quit and
   /* Decode the first argument: find the window or frame to use.  */
   if (EQ (position, Qt)
       || (CONSP (position) && (EQ (XCAR (position), Qmenu_bar)
+                              || EQ (XCAR (position), Qtab_bar)
                               || EQ (XCAR (position), Qtool_bar))))
     window = selected_window;
   else if (CONSP (position))
diff --git a/src/msdos.c b/src/msdos.c
index d13f230..1192b37 100644
--- a/src/msdos.c
+++ b/src/msdos.c
@@ -2655,7 +2655,7 @@ dos_rawgetc (void)
              static Lisp_Object last_mouse_window;
 
              mouse_window = window_from_coordinates
-               (SELECTED_FRAME (), mouse_last_x, mouse_last_y, 0, 0);
+               (SELECTED_FRAME (), mouse_last_x, mouse_last_y, 0, 0, 0);
              /* A window will be selected only when it is not
                 selected now, and the last mouse movement event was
                 not in it.  A minibuffer window will be selected iff
diff --git a/src/termhooks.h b/src/termhooks.h
index f182712..4830a85 100644
--- a/src/termhooks.h
+++ b/src/termhooks.h
@@ -194,6 +194,11 @@ enum event_kind
      the help to show.  */
   HELP_EVENT,
 
+  /* An event from a tab-bar.  Member `arg' of the input event
+     contains the tab-bar item selected.  If `frame_or_window'
+     and `arg' are equal, this is a prefix event.  */
+  TAB_BAR_EVENT,
+
   /* An event from a tool-bar.  Member `arg' of the input event
      contains the tool-bar item selected.  If `frame_or_window'
      and `arg' are equal, this is a prefix event.  */
@@ -624,6 +629,9 @@ struct terminal
   Lisp_Object (*popup_dialog_hook) (struct frame *f, Lisp_Object header,
                                    Lisp_Object contents);
 
+  /* This hook is called to change the frame's (internal) tab-bar.  */
+  void (*change_tab_bar_height_hook) (struct frame *f, int height);
+
   /* This hook is called to change the frame's (internal) tool-bar.  */
   void (*change_tool_bar_height_hook) (struct frame *f, int height);
 
diff --git a/src/w32fns.c b/src/w32fns.c
index d6fd8f5..4b95b25 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -6000,7 +6000,7 @@ DEFUN ("x-create-frame", Fx_create_frame, Sx_create_frame,
 
   f->output_data.w32->current_cursor = f->output_data.w32->nontext_cursor;
 
-  window_prompting = gui_figure_window_size (f, parameters, true,
+  window_prompting = gui_figure_window_size (f, parameters, true, true,
                                              &x_width, &x_height);
 
   tem = gui_display_get_arg (dpyinfo, parameters, Qunsplittable, 0, 0,
@@ -6968,7 +6968,7 @@ w32_create_tip_frame (struct w32_display_info *dpyinfo, 
Lisp_Object parms)
   f->output_data.w32->parent_desc = FRAME_DISPLAY_INFO (f)->root_window;
   f->output_data.w32->explicit_parent = false;
 
-  gui_figure_window_size (f, parms, true, &x_width, &x_height);
+  gui_figure_window_size (f, parms, true, true, &x_width, &x_height);
 
   /* No fringes on tip frame.  */
   f->fringe_cols = 0;
@@ -10193,6 +10193,7 @@ frame_parm_handler w32_frame_parm_handlers[] =
   gui_set_vertical_scroll_bars,
   gui_set_horizontal_scroll_bars,
   gui_set_visibility,
+  w32_set_tab_bar_lines,
   w32_set_tool_bar_lines,
   0, /* x_set_scroll_bar_foreground, */
   0, /* x_set_scroll_bar_background, */
diff --git a/src/w32inevt.c b/src/w32inevt.c
index fc1f90c..2b6979b 100644
--- a/src/w32inevt.c
+++ b/src/w32inevt.c
@@ -492,7 +492,7 @@ do_mouse_event (MOUSE_EVENT_RECORD *event,
            if (!NILP (Vmouse_autoselect_window))
              {
                Lisp_Object mouse_window = window_from_coordinates (f, mx, my,
-                                                                   0, 0);
+                                                                   0, 0, 0);
                /* A window will be selected only when it is not
                   selected now, and the last mouse movement event was
                   not in it.  A minibuffer window will be selected iff
diff --git a/src/w32term.c b/src/w32term.c
index e5874f2..82c7e21 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -4998,7 +4998,7 @@ w32_read_socket (struct terminal *terminal,
                {
                  static Lisp_Object last_mouse_window;
                  Lisp_Object window = window_from_coordinates
-                   (f, LOWORD (msg.msg.lParam), HIWORD (msg.msg.lParam), 0, 0);
+                   (f, LOWORD (msg.msg.lParam), HIWORD (msg.msg.lParam), 0, 0, 
0);
 
                  /* Window will be selected only when it is not
                     selected now and last mouse movement event was
@@ -5068,7 +5068,7 @@ w32_read_socket (struct terminal *terminal,
                    int x = XFIXNAT (inev.x);
                    int y = XFIXNAT (inev.y);
 
-                    window = window_from_coordinates (f, x, y, 0, 1);
+                    window = window_from_coordinates (f, x, y, 0, 1, 0);
 
                     if (EQ (window, f->tool_bar_window))
                       {
@@ -5936,7 +5936,7 @@ w32_draw_window_cursor (struct window *w, struct 
glyph_row *glyph_row,
            = (WINDOW_TO_FRAME_PIXEL_Y (w, w->phys_cursor.y)
               + glyph_row->ascent - w->phys_cursor_ascent);
          w32_system_caret_window = w;
-         w32_system_caret_hdr_height = WINDOW_HEADER_LINE_HEIGHT (w);
+         w32_system_caret_hdr_height = WINDOW_TAB_LINE_HEIGHT (w) + 
WINDOW_HEADER_LINE_HEIGHT (w);
          w32_system_caret_mode_height = WINDOW_MODE_LINE_HEIGHT (w);
 
          PostMessage (hwnd, WM_IME_STARTCOMPOSITION, 0, 0);
diff --git a/src/window.c b/src/window.c
index 9a0a9a1..30b53d1 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1002,6 +1002,7 @@ static int
 window_body_height (struct window *w, bool pixelwise)
 {
   int height = (w->pixel_height
+               - WINDOW_TAB_LINE_HEIGHT (w)
                - WINDOW_HEADER_LINE_HEIGHT (w)
                - (WINDOW_HAS_HORIZONTAL_SCROLL_BAR (w)
                   ? WINDOW_SCROLL_BAR_AREA_HEIGHT (w)
@@ -1131,6 +1132,15 @@ WINDOW must be a live window and defaults to the 
selected one.  */)
   return (make_fixnum (WINDOW_HEADER_LINE_HEIGHT (decode_live_window 
(window))));
 }
 
+DEFUN ("window-tab-line-height", Fwindow_tab_line_height,
+       Swindow_tab_line_height, 0, 1, 0,
+       doc: /* Return the height in pixels of WINDOW's tab-line.
+WINDOW must be a live window and defaults to the selected one.  */)
+  (Lisp_Object window)
+{
+  return (make_fixnum (WINDOW_TAB_LINE_HEIGHT (decode_live_window (window))));
+}
+
 DEFUN ("window-right-divider-width", Fwindow_right_divider_width,
        Swindow_right_divider_width, 0, 1, 0,
        doc: /* Return the width in pixels of WINDOW's right divider.
@@ -1249,7 +1259,8 @@ end-trigger value is reset to nil.  */)
    if it is on the border between the window and its right sibling,
       return ON_VERTICAL_BORDER;
    if it is on a scroll bar, return ON_SCROLL_BAR;
-   if it is on the window's top line, return ON_HEADER_LINE;
+   if it is on the window's top line, return ON_TAB_LINE;
+   if it is on the window's header line, return ON_HEADER_LINE;
    if it is in left or right fringe of the window,
       return ON_LEFT_FRINGE or ON_RIGHT_FRINGE;
    if it is in the marginal area to the left/right of the window,
@@ -1299,15 +1310,18 @@ coordinates_in_window (register struct window *w, int 
x, int y)
                     - CURRENT_MODE_LINE_HEIGHT (w)
                     - WINDOW_BOTTOM_DIVIDER_WIDTH (w))))
     return ON_HORIZONTAL_SCROLL_BAR;
-  /* On the mode or header line?   */
+  /* On the mode or header/tab line?   */
   else if ((window_wants_mode_line (w)
            && y >= (bottom_y
                     - CURRENT_MODE_LINE_HEIGHT (w)
                     - WINDOW_BOTTOM_DIVIDER_WIDTH (w))
            && y <= bottom_y - WINDOW_BOTTOM_DIVIDER_WIDTH (w)
            && (part = ON_MODE_LINE))
+          || (window_wants_tab_line (w)
+              && y < top_y + CURRENT_TAB_LINE_HEIGHT (w)
+              && (part = ON_TAB_LINE))
           || (window_wants_header_line (w)
-              && y < top_y + CURRENT_HEADER_LINE_HEIGHT (w)
+              && y < top_y + CURRENT_TAB_LINE_HEIGHT (w) + 
CURRENT_HEADER_LINE_HEIGHT (w)
               && (part = ON_HEADER_LINE)))
     {
       /* If it's under/over the scroll bar portion of the mode/header
@@ -1407,6 +1421,7 @@ window_relative_x_coord (struct window *w, enum 
window_part part, int x)
     case ON_TEXT:
       return x - window_box_left (w, TEXT_AREA);
 
+    case ON_TAB_LINE:
     case ON_HEADER_LINE:
     case ON_MODE_LINE:
     case ON_LEFT_FRINGE:
@@ -1457,6 +1472,7 @@ If they are in the bottom divider of WINDOW, 
`bottom-divider' is returned.
 If they are in the right divider of WINDOW, `right-divider' is returned.
 If they are in the mode line of WINDOW, `mode-line' is returned.
 If they are in the header line of WINDOW, `header-line' is returned.
+If they are in the tab line of WINDOW, `tab-line' is returned.
 If they are in the left fringe of WINDOW, `left-fringe' is returned.
 If they are in the right fringe of WINDOW, `right-fringe' is returned.
 If they are on the border between WINDOW and its right sibling,
@@ -1502,6 +1518,9 @@ If they are in the windows's left or right marginal 
areas, `left-margin'\n\
     case ON_HEADER_LINE:
       return Qheader_line;
 
+    case ON_TAB_LINE:
+      return Qtab_line;
+
     case ON_LEFT_FRINGE:
       return Qleft_fringe;
 
@@ -1585,7 +1604,7 @@ check_window_containing (struct window *w, void 
*user_data)
 
 Lisp_Object
 window_from_coordinates (struct frame *f, int x, int y,
-                        enum window_part *part, bool tool_bar_p)
+                        enum window_part *part, bool tab_bar_p, bool 
tool_bar_p)
 {
   Lisp_Object window;
   struct check_window_data cw;
@@ -1598,6 +1617,21 @@ window_from_coordinates (struct frame *f, int x, int y,
   cw.window = &window, cw.x = x, cw.y = y; cw.part = part;
   foreach_window (f, check_window_containing, &cw);
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  /* If not found above, see if it's in the tab bar window, if a tab
+     bar exists.  */
+  if (NILP (window)
+      && tab_bar_p
+      && WINDOWP (f->tab_bar_window)
+      && WINDOW_TOTAL_LINES (XWINDOW (f->tab_bar_window)) > 0
+      && (coordinates_in_window (XWINDOW (f->tab_bar_window), x, y)
+         != ON_NOTHING))
+    {
+      *part = ON_TEXT;
+      window = f->tab_bar_window;
+    }
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   /* If not found above, see if it's in the tool bar window, if a tool
      bar exists.  */
@@ -1633,7 +1667,7 @@ column 0.  */)
                                   + FRAME_INTERNAL_BORDER_WIDTH (f)),
                                  (FRAME_PIXEL_Y_FROM_CANON_Y (f, y)
                                   + FRAME_INTERNAL_BORDER_WIDTH (f)),
-                                 0, false);
+                                 0, false, false);
 }
 
 DEFUN ("window-point", Fwindow_point, Swindow_point, 0, 1, 0,
@@ -1945,6 +1979,14 @@ Return nil if window display is not up-to-date.  In that 
case, use
       goto found_row;
     }
 
+  if (EQ (line, Qtab_line))
+    {
+      if (!window_wants_tab_line (w))
+       return Qnil;
+      row = MATRIX_TAB_LINE_ROW (w->current_matrix);
+      return row->enabled_p ? list4i (row->height, 0, 0, 0) : Qnil;
+    }
+
   if (EQ (line, Qheader_line))
     {
       if (!window_wants_header_line (w))
@@ -1959,7 +2001,8 @@ Return nil if window display is not up-to-date.  In that 
case, use
       return (row->enabled_p ?
              list4i (row->height,
                      0, /* not accurate */
-                     (WINDOW_HEADER_LINE_HEIGHT (w)
+                     (WINDOW_TAB_LINE_HEIGHT (w)
+                      + WINDOW_HEADER_LINE_HEIGHT (w)
                       + window_text_bottom_y (w)),
                      0)
              : Qnil);
@@ -2045,8 +2088,9 @@ though when run from an idle timer with a delay of zero 
seconds.  */)
   int max_y = NILP (body) ? WINDOW_PIXEL_HEIGHT (w) : window_text_bottom_y (w);
   Lisp_Object rows = Qnil;
   int window_width = NILP (body) ? w->pixel_width : window_body_width (w, 
true);
+  int tab_line_height = WINDOW_TAB_LINE_HEIGHT (w);
   int header_line_height = WINDOW_HEADER_LINE_HEIGHT (w);
-  int subtract = NILP (body) ? 0 : header_line_height;
+  int subtract = NILP (body) ? 0 : (tab_line_height + header_line_height);
   bool invert = !NILP (inverse);
   bool left_flag = !NILP (left);
 
@@ -4246,7 +4290,7 @@ make_window (void)
      non-Lisp data, so do it only for slots which should not be zero.  */
   w->nrows_scale_factor = w->ncols_scale_factor = 1;
   w->left_fringe_width = w->right_fringe_width = -1;
-  w->mode_line_height = w->header_line_height = -1;
+  w->mode_line_height = w->tab_line_height = w->header_line_height = -1;
 #ifdef HAVE_WINDOW_SYSTEM
   w->phys_cursor_type = NO_CURSOR;
   w->phys_cursor_width = -1;
@@ -4772,7 +4816,7 @@ Third argument SIDE nil (or `below') specifies that the 
new window shall
 be located below WINDOW.  SIDE `above' means the new window shall be
 located above WINDOW.  In both cases PIXEL-SIZE specifies the pixel
 height of the new window including space reserved for the mode and/or
-header line.
+header/tab line.
 
 SIDE t (or `right') specifies that the new window shall be located on
 the right side of WINDOW.  SIDE `left' means the new window shall be
@@ -5350,6 +5394,40 @@ window_wants_header_line (struct window *w)
          : 0);
 }
 
+
+/**
+ * window_wants_tab_line:
+ *
+ * Return 1 if window W wants a tab line and is high enough to
+ * accommodate it, 0 otherwise.
+ *
+ * W wants a tab line if it's a leaf window and neither a minibuffer
+ * nor a pseudo window.  Moreover, its 'window-mode-line-format'
+ * parameter must not be 'none' and either that parameter or W's
+ * buffer's 'mode-line-format' value must be non-nil.  Finally, W must
+ * be higher than its frame's canonical character height and be able
+ * to accommodate a mode line and a header line too if necessary (the
+ * mode line and a header line prevail).
+ */
+bool
+window_wants_tab_line (struct window *w)
+{
+  Lisp_Object window_tab_line_format =
+    window_parameter (w, Qtab_line_format);
+
+  return ((WINDOW_LEAF_P (w)
+          && !MINI_WINDOW_P (w)
+          && !WINDOW_PSEUDO_P (w)
+          && !EQ (window_tab_line_format, Qnone)
+          && !NILP (window_tab_line_format)
+          && (WINDOW_PIXEL_HEIGHT (w)
+              > (((window_wants_mode_line (w) ? 1 : 0)
+                   + (window_wants_header_line (w) ? 1 : 0)
+                   + 1) * WINDOW_FRAME_LINE_HEIGHT (w))))
+         ? 1
+         : 0);
+}
+
 /* Return number of lines of text in window W, not counting the mode
    line and header line, if any.  Do NOT use this for windows on GUI
    frames; use window_body_height instead.  This function is only for
@@ -5366,6 +5444,9 @@ window_internal_height (struct window *w)
   if (window_wants_header_line (w))
     --ht;
 
+  if (window_wants_tab_line (w))
+    --ht;
+
   return ht;
 }
 
@@ -5726,7 +5807,7 @@ window_scroll_pixel_based (Lisp_Object window, int n, 
bool whole, bool noerror)
       move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
       if (IT_CHARPOS (it) == PT
          && it.current_y >= this_scroll_margin
-         && it.current_y <= last_y - WINDOW_HEADER_LINE_HEIGHT (w)
+         && it.current_y <= last_y - WINDOW_TAB_LINE_HEIGHT (w) - 
WINDOW_HEADER_LINE_HEIGHT (w)
           && (NILP (Vscroll_preserve_screen_position)
              || EQ (Vscroll_preserve_screen_position, Qt)))
        /* We found PT at a legitimate height.  Leave it alone.  */
@@ -5742,7 +5823,7 @@ window_scroll_pixel_based (Lisp_Object window, int n, 
bool whole, bool noerror)
                 is necessary because we set it.current_y to 0, above.  */
              move_it_to (&it, -1,
                          window_scroll_pixel_based_preserve_x,
-                         goal_y - WINDOW_HEADER_LINE_HEIGHT (w),
+                         goal_y - WINDOW_TAB_LINE_HEIGHT (w) - 
WINDOW_HEADER_LINE_HEIGHT (w),
                          -1, MOVE_TO_Y | MOVE_TO_X);
            }
 
@@ -5778,7 +5859,7 @@ window_scroll_pixel_based (Lisp_Object window, int n, 
bool whole, bool noerror)
                  /* We subtract WINDOW_HEADER_LINE_HEIGHT because
                     it.y is relative to the bottom of the header
                     line, see above.  */
-                 (it.last_visible_y - WINDOW_HEADER_LINE_HEIGHT (w)
+                 (it.last_visible_y - WINDOW_TAB_LINE_HEIGHT (w) - 
WINDOW_HEADER_LINE_HEIGHT (w)
                    - partial_line_height (&it) - this_scroll_margin - 1),
                  -1,
                  MOVE_TO_POS | MOVE_TO_Y);
@@ -5817,13 +5898,13 @@ window_scroll_pixel_based (Lisp_Object window, int n, 
bool whole, bool noerror)
       if (it.what == IT_EOB)
        partial_p =
          it.current_y + it.ascent + it.descent
-         > it.last_visible_y - this_scroll_margin - WINDOW_HEADER_LINE_HEIGHT 
(w);
+         > it.last_visible_y - this_scroll_margin - WINDOW_TAB_LINE_HEIGHT (w) 
- WINDOW_HEADER_LINE_HEIGHT (w);
       else
        {
          move_it_by_lines (&it, 1);
          partial_p =
            it.current_y
-           > it.last_visible_y - this_scroll_margin - 
WINDOW_HEADER_LINE_HEIGHT (w);
+           > it.last_visible_y - this_scroll_margin - WINDOW_TAB_LINE_HEIGHT 
(w) - WINDOW_HEADER_LINE_HEIGHT (w);
        }
 
       if (charpos == PT && !partial_p
@@ -6370,6 +6451,9 @@ and redisplay normally--don't erase and redraw the frame. 
 */)
          /* Invalidate pixel data calculated for all compositions.  */
          for (i = 0; i < n_compositions; i++)
            composition_table[i]->font = NULL;
+#if defined (HAVE_WINDOW_SYSTEM)
+         WINDOW_XFRAME (w)->minimize_tab_bar_window_p = 1;
+#endif
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
          WINDOW_XFRAME (w)->minimize_tool_bar_window_p = 1;
 #endif
@@ -6686,13 +6770,13 @@ struct save_window_data
 
     /* We should be able to do without the following two.  */
     int frame_cols, frame_lines;
-    /* These two should get eventually replaced by their pixel
+    /* These three should get eventually replaced by their pixel
        counterparts.  */
-    int frame_menu_bar_lines, frame_tool_bar_lines;
+    int frame_menu_bar_lines, frame_tab_bar_lines, frame_tool_bar_lines;
     int frame_text_width, frame_text_height;
     /* These are currently unused.  We need them as soon as we convert
        to pixels.  */
-    int frame_menu_bar_height, frame_tool_bar_height;
+    int frame_menu_bar_height, frame_tab_bar_height, frame_tool_bar_height;
   } GCALIGNED_STRUCT;
 
 /* This is saved as a Lisp_Vector.  */
@@ -7370,10 +7454,12 @@ saved by this function.  */)
   data->frame_cols = FRAME_COLS (f);
   data->frame_lines = FRAME_LINES (f);
   data->frame_menu_bar_lines = FRAME_MENU_BAR_LINES (f);
+  data->frame_tab_bar_lines = FRAME_TAB_BAR_LINES (f);
   data->frame_tool_bar_lines = FRAME_TOOL_BAR_LINES (f);
   data->frame_text_width = FRAME_TEXT_WIDTH (f);
   data->frame_text_height = FRAME_TEXT_HEIGHT (f);
   data->frame_menu_bar_height = FRAME_MENU_BAR_HEIGHT (f);
+  data->frame_tab_bar_height = FRAME_TAB_BAR_HEIGHT (f);
   data->frame_tool_bar_height = FRAME_TOOL_BAR_HEIGHT (f);
   data->selected_frame = selected_frame;
   data->current_window = FRAME_SELECTED_WINDOW (f);
@@ -7663,6 +7749,7 @@ set_window_scroll_bars (struct window *w, Lisp_Object 
width,
 
       /* Don't change anything if new scroll bar won't fit.  */
       if ((WINDOW_PIXEL_HEIGHT (w)
+          - WINDOW_TAB_LINE_HEIGHT (w)
           - WINDOW_HEADER_LINE_HEIGHT (w)
           - WINDOW_MODE_LINE_HEIGHT (w)
           - (new_height == -1 ? FRAME_SCROLL_BAR_AREA_HEIGHT (f) : new_height))
@@ -8086,6 +8173,7 @@ syms_of_window (void)
   DEFSYM (Qmark_for_redisplay, "mark-for-redisplay");
   DEFSYM (Qmode_line_format, "mode-line-format");
   DEFSYM (Qheader_line_format, "header-line-format");
+  DEFSYM (Qtab_line_format, "tab-line-format");
 
   DEFVAR_LISP ("temp-buffer-show-function", Vtemp_buffer_show_function,
               doc: /* Non-nil means call as function to display a help buffer.
@@ -8389,6 +8477,7 @@ displayed after a scrolling operation to be somewhat 
inaccurate.  */);
   defsubr (&Sset_window_redisplay_end_trigger);
   defsubr (&Swindow_mode_line_height);
   defsubr (&Swindow_header_line_height);
+  defsubr (&Swindow_tab_line_height);
   defsubr (&Swindow_right_divider_width);
   defsubr (&Swindow_bottom_divider_width);
   defsubr (&Swindow_scroll_bar_width);
diff --git a/src/window.h b/src/window.h
index dfbc638..2683c6b 100644
--- a/src/window.h
+++ b/src/window.h
@@ -361,6 +361,9 @@ struct window
     /* Effective height of the header line, or -1 if not known.  */
     int header_line_height;
 
+    /* Effective height of the tab line, or -1 if not known.  */
+    int tab_line_height;
+
     /* Z - the buffer position of the last glyph in the current
        matrix of W.  Only valid if window_end_valid is true.  */
     ptrdiff_t window_end_pos;
@@ -697,7 +700,7 @@ wset_next_buffers (struct window *w, Lisp_Object val)
   (WINDOW_LEFT_EDGE_COL (W) + WINDOW_TOTAL_COLS (W))
 
 /* Return the canonical frame line at which window W starts.
-   This includes a header line, if any.  */
+   This includes a header/tab line, if any.  */
 #define WINDOW_TOP_EDGE_LINE(W) (W)->top_line
 
 /* Return the canonical frame line before which window W ends.
@@ -715,7 +718,7 @@ wset_next_buffers (struct window *w, Lisp_Object val)
   (WINDOW_LEFT_PIXEL_EDGE (W) + WINDOW_PIXEL_WIDTH (W))
 
 /* Return the top pixel edge at which window W starts.
-   This includes a header line, if any.  */
+   This includes a header/tab line, if any.  */
 #define WINDOW_TOP_PIXEL_EDGE(W) (W)->pixel_top
 
 /* Return the bottom pixel edge before which window W ends.
@@ -745,6 +748,13 @@ wset_next_buffers (struct window *w, Lisp_Object val)
 #define WINDOW_MENU_BAR_P(W) false
 #endif
 
+/* True if W is a tab bar window.  */
+#if defined (HAVE_WINDOW_SYSTEM)
+#define WINDOW_TAB_BAR_P(W) \
+  (WINDOWP (WINDOW_XFRAME (W)->tab_bar_window) \
+   && (W) == XWINDOW (WINDOW_XFRAME (W)->tab_bar_window))
+#endif
+
 /* True if W is a tool bar window.  */
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
 #define WINDOW_TOOL_BAR_P(W) \
@@ -756,13 +766,13 @@ wset_next_buffers (struct window *w, Lisp_Object val)
 
 /* Return the frame y-position at which window W starts.  */
 #define WINDOW_TOP_EDGE_Y(W) \
-  (((WINDOW_MENU_BAR_P (W) || WINDOW_TOOL_BAR_P (W)) \
+  (((WINDOW_MENU_BAR_P (W) || WINDOW_TAB_BAR_P (W) || WINDOW_TOOL_BAR_P (W)) \
     ? 0 : FRAME_INTERNAL_BORDER_WIDTH (WINDOW_XFRAME (W))) \
    + WINDOW_TOP_PIXEL_EDGE (W))
 
 /* Return the frame y-position before which window W ends.  */
 #define WINDOW_BOTTOM_EDGE_Y(W)                                   \
-  (((WINDOW_MENU_BAR_P (W) || WINDOW_TOOL_BAR_P (W))      \
+  (((WINDOW_MENU_BAR_P (W) || WINDOW_TAB_BAR_P (W) || WINDOW_TOOL_BAR_P (W))   
   \
     ? 0 : FRAME_INTERNAL_BORDER_WIDTH (WINDOW_XFRAME (W))) \
    + WINDOW_BOTTOM_PIXEL_EDGE (W))
 
@@ -996,6 +1006,16 @@ wset_next_buffers (struct window *w, Lisp_Object val)
 #define WINDOW_HEADER_LINE_LINES(W)    \
   window_wants_header_line (W)
 
+/* Height in pixels of the tab line.
+   Zero if W doesn't have a tab line.  */
+#define WINDOW_TAB_LINE_HEIGHT(W)      \
+  (window_wants_tab_line (W)           \
+   ? CURRENT_TAB_LINE_HEIGHT (W)       \
+   : 0)
+
+#define WINDOW_TAB_LINE_LINES(W)       \
+  window_wants_tab_line (W)
+
 /* Pixel height of window W without mode line, bottom scroll bar and
    bottom divider.  */
 #define WINDOW_BOX_HEIGHT_NO_MODE_LINE(W)      \
@@ -1004,14 +1024,15 @@ wset_next_buffers (struct window *w, Lisp_Object val)
    - WINDOW_SCROLL_BAR_AREA_HEIGHT (W)         \
    - WINDOW_MODE_LINE_HEIGHT (W))
 
-/* Pixel height of window W without mode and header line and bottom
+/* Pixel height of window W without mode and header/tab line and bottom
    divider.  */
 #define WINDOW_BOX_TEXT_HEIGHT(W)      \
   (WINDOW_PIXEL_HEIGHT ((W))           \
    - WINDOW_BOTTOM_DIVIDER_WIDTH (W)   \
    - WINDOW_SCROLL_BAR_AREA_HEIGHT (W) \
    - WINDOW_MODE_LINE_HEIGHT (W)       \
-   - WINDOW_HEADER_LINE_HEIGHT (W))
+   - WINDOW_HEADER_LINE_HEIGHT (W)     \
+   - WINDOW_TAB_LINE_HEIGHT (W))
 
 /* Return the frame position where the horizontal scroll bar of window W
    starts.  */
@@ -1068,7 +1089,7 @@ extern Lisp_Object minibuf_selected_window;
 
 extern Lisp_Object make_window (void);
 extern Lisp_Object window_from_coordinates (struct frame *, int, int,
-                                            enum window_part *, bool);
+                                            enum window_part *, bool, bool);
 extern void resize_frame_windows (struct frame *, int, bool);
 extern void restore_window_configuration (Lisp_Object);
 extern void delete_all_child_windows (Lisp_Object);
@@ -1158,6 +1179,7 @@ extern bool compare_window_configurations (Lisp_Object, 
Lisp_Object, bool);
 extern void mark_window_cursors_off (struct window *);
 extern bool window_wants_mode_line (struct window *);
 extern bool window_wants_header_line (struct window *);
+extern bool window_wants_tab_line (struct window *);
 extern int window_internal_height (struct window *);
 extern int window_body_width (struct window *w, bool);
 enum margin_unit { MARGIN_IN_LINES, MARGIN_IN_PIXELS };
diff --git a/src/xdisp.c b/src/xdisp.c
index 75bc536..e61d8f7 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -989,6 +989,7 @@ static int underlying_face_id (struct it *);
 
 #ifdef HAVE_WINDOW_SYSTEM
 
+static void update_tab_bar (struct frame *, bool);
 static void update_tool_bar (struct frame *, bool);
 static void gui_draw_bottom_divider (struct window *w);
 static void notice_overwritten_cursor (struct window *,
@@ -1080,7 +1081,7 @@ window_box_height (struct window *w)
   height -= WINDOW_BOTTOM_DIVIDER_WIDTH (w);
   height -= WINDOW_SCROLL_BAR_AREA_HEIGHT (w);
 
-  /* Note: the code below that determines the mode-line/header-line
+  /* Note: the code below that determines the mode-line/header-line/tab-line
      height is essentially the same as that contained in the macro
      CURRENT_{MODE,HEADER}_LINE_HEIGHT, except that it checks whether
      the appropriate glyph row has its `mode_line_p' flag set,
@@ -1098,6 +1099,18 @@ window_box_height (struct window *w)
        height -= estimate_mode_line_height (f, CURRENT_MODE_LINE_FACE_ID (w));
     }
 
+  if (window_wants_tab_line (w))
+    {
+      struct glyph_row *tl_row
+       = (w->current_matrix && w->current_matrix->rows
+          ? MATRIX_TAB_LINE_ROW (w->current_matrix)
+          : 0);
+      if (tl_row && tl_row->mode_line_p)
+       height -= tl_row->height;
+      else
+       height -= estimate_mode_line_height (f, TAB_LINE_FACE_ID);
+    }
+
   if (window_wants_header_line (w))
     {
       struct glyph_row *hl_row
@@ -1210,6 +1223,8 @@ window_box (struct window *w, enum glyph_row_area area, 
int *box_x,
   if (box_y)
     {
       *box_y = WINDOW_TOP_EDGE_Y (w);
+      if (window_wants_tab_line (w))
+       *box_y += CURRENT_TAB_LINE_HEIGHT (w);
       if (window_wants_header_line (w))
        *box_y += CURRENT_HEADER_LINE_HEIGHT (w);
     }
@@ -1435,13 +1450,14 @@ pos_visible_p (struct window *w, ptrdiff_t charpos, int 
*x, int *y,
 
   /* Some Lisp hook could call us in the middle of redisplaying this
      very window.  If, by some bad luck, we are retrying redisplay
-     because we found that the mode-line height and/or header-line
+     because we found that the mode-line height and/or tab/header-line
      height needs to be updated, the assignment of mode_line_height
      and header_line_height below could disrupt that, due to the
      selected/nonselected window dance during mode-line display, and
      we could infloop.  Avoid that.  */
   int prev_mode_line_height = w->mode_line_height;
   int prev_header_line_height = w->header_line_height;
+  int prev_tab_line_height = w->tab_line_height;
   /* Compute exact mode line heights.  */
   if (window_wants_mode_line (w))
     {
@@ -1455,6 +1471,15 @@ pos_visible_p (struct window *w, ptrdiff_t charpos, int 
*x, int *y,
                             : window_mode_line_format);
     }
 
+  if (window_wants_tab_line (w))
+    {
+      Lisp_Object window_tab_line_format
+       = window_parameter (w, Qtab_line_format);
+
+      w->tab_line_height
+       = display_mode_line (w, TAB_LINE_FACE_ID, window_tab_line_format);
+    }
+
   if (window_wants_header_line (w))
     {
       Lisp_Object window_header_line_format
@@ -1511,7 +1536,7 @@ pos_visible_p (struct window *w, ptrdiff_t charpos, int 
*x, int *y,
         glyph.  */
       int top_x = it.current_x;
       int top_y = it.current_y;
-      int window_top_y = WINDOW_HEADER_LINE_HEIGHT (w);
+      int window_top_y = WINDOW_TAB_LINE_HEIGHT (w) + 
WINDOW_HEADER_LINE_HEIGHT (w);
       int bottom_y;
       struct it save_it;
       void *save_it_data = NULL;
@@ -1779,7 +1804,8 @@ pos_visible_p (struct window *w, ptrdiff_t charpos, int 
*x, int *y,
                           - it.last_visible_y));
          *rowh = max (0, (min (it2.current_y + it2.max_ascent + 
it2.max_descent,
                                it.last_visible_y)
-                          - max (it2.current_y,
+                          - max (max (it2.current_y,
+                                       WINDOW_TAB_LINE_HEIGHT (w)),
                                  WINDOW_HEADER_LINE_HEIGHT (w))));
          *vpos = it2.vpos;
          if (it2.bidi_it.paragraph_dir == R2L)
@@ -1820,6 +1846,7 @@ pos_visible_p (struct window *w, ptrdiff_t charpos, int 
*x, int *y,
   /* Restore potentially overwritten values.  */
   w->mode_line_height = prev_mode_line_height;
   w->header_line_height = prev_header_line_height;
+  w->tab_line_height = prev_tab_line_height;
 
   return visible_p;
 }
@@ -2212,7 +2239,7 @@ get_glyph_string_clip_rects (struct glyph_string *s, 
NativeRectangle *rects, int
      intentionally draws over other lines.  */
   if (s->for_overlaps)
     {
-      r.y = WINDOW_HEADER_LINE_HEIGHT (s->w);
+      r.y = WINDOW_TAB_LINE_HEIGHT (s->w) + WINDOW_HEADER_LINE_HEIGHT (s->w);
       r.height = window_text_bottom_y (s->w) - r.y;
 
       /* Alas, the above simple strategy does not work for the
@@ -2239,7 +2266,7 @@ get_glyph_string_clip_rects (struct glyph_string *s, 
NativeRectangle *rects, int
         partially visible lines at the top of a window.  */
       if (!s->row->full_width_p
          && MATRIX_ROW_PARTIALLY_VISIBLE_AT_TOP_P (s->w, s->row))
-       r.y = WINDOW_HEADER_LINE_HEIGHT (s->w);
+       r.y = WINDOW_TAB_LINE_HEIGHT (s->w) + WINDOW_HEADER_LINE_HEIGHT (s->w);
       else
        r.y = max (0, s->row->y);
     }
@@ -2416,7 +2443,7 @@ get_phys_cursor_geometry (struct window *w, struct 
glyph_row *row,
   h = min (h, row->height);
   h0 = min (h0, ascent + glyph->descent);
 
-  y0 = WINDOW_HEADER_LINE_HEIGHT (w);
+  y0 = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w);
   if (y < y0)
     {
       h = max (h - (y0 - y) + 1, h0);
@@ -2460,7 +2487,7 @@ remember_mouse_glyph (struct frame *f, int gx, int gy, 
NativeRectangle *rect)
       goto virtual_glyph;
     }
   else if (!f->glyphs_initialized_p
-          || (window = window_from_coordinates (f, gx, gy, &part, false),
+          || (window = window_from_coordinates (f, gx, gy, &part, false, 
false),
               NILP (window)))
     {
       width = FRAME_SMALLEST_CHAR_WIDTH (f);
@@ -2495,11 +2522,14 @@ remember_mouse_glyph (struct frame *f, int gx, int gy, 
NativeRectangle *rect)
       area = RIGHT_MARGIN_AREA;
       goto text_glyph;
 
+    case ON_TAB_LINE:
     case ON_HEADER_LINE:
     case ON_MODE_LINE:
-      gr = (part == ON_HEADER_LINE
-           ? MATRIX_HEADER_LINE_ROW (w->current_matrix)
-           : MATRIX_MODE_LINE_ROW (w->current_matrix));
+      gr = (part == ON_TAB_LINE
+           ? MATRIX_TAB_LINE_ROW (w->current_matrix)
+           : (part == ON_HEADER_LINE
+               ? MATRIX_HEADER_LINE_ROW (w->current_matrix)
+               : MATRIX_MODE_LINE_ROW (w->current_matrix)));
       gy = gr->y;
       area = TEXT_AREA;
       goto text_glyph_row_found;
@@ -2545,7 +2575,7 @@ remember_mouse_glyph (struct frame *f, int gx, int gy, 
NativeRectangle *rect)
              gx += (x / width) * width;
            }
 
-         if (part != ON_MODE_LINE && part != ON_HEADER_LINE)
+         if (part != ON_MODE_LINE && part != ON_HEADER_LINE && part != 
ON_TAB_LINE)
            {
              gx += window_box_left_offset (w, area);
              /* Don't expand over the modeline to make sure the vertical
@@ -2560,7 +2590,7 @@ remember_mouse_glyph (struct frame *f, int gx, int gy, 
NativeRectangle *rect)
          gx = (x / width) * width;
          y -= gy;
          gy += (y / height) * height;
-         if (part != ON_MODE_LINE && part != ON_HEADER_LINE)
+         if (part != ON_MODE_LINE && part != ON_HEADER_LINE && part != 
ON_TAB_LINE)
            /* See comment above.  */
            height = min (height,
                          max (0, WINDOW_BOX_HEIGHT_NO_MODE_LINE (w) - gy));
@@ -2920,6 +2950,8 @@ init_iterator (struct it *it, struct window *w,
       if (base_face_id == MODE_LINE_FACE_ID
          || base_face_id == MODE_LINE_INACTIVE_FACE_ID)
        row = MATRIX_MODE_LINE_ROW (w->desired_matrix);
+      else if (base_face_id == TAB_LINE_FACE_ID)
+       row = MATRIX_TAB_LINE_ROW (w->desired_matrix);
       else if (base_face_id == HEADER_LINE_FACE_ID)
        row = MATRIX_HEADER_LINE_ROW (w->desired_matrix);
     }
@@ -3097,8 +3129,9 @@ init_iterator (struct it *it, struct window *w,
            it->last_visible_x -= it->continuation_pixel_width;
        }
 
+      it->tab_line_p = window_wants_tab_line (w);
       it->header_line_p = window_wants_header_line (w);
-      body_height = WINDOW_HEADER_LINE_HEIGHT (w);
+      body_height = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w);
       it->current_y =  body_height + w->vscroll;
     }
 
@@ -3201,7 +3234,7 @@ void
 start_display (struct it *it, struct window *w, struct text_pos pos)
 {
   struct glyph_row *row;
-  bool first_vpos = window_wants_header_line (w);
+  int first_vpos = window_wants_tab_line (w) + window_wants_header_line (w);
 
   row = w->desired_matrix->rows + first_vpos;
   init_iterator (it, w, CHARPOS (pos), BYTEPOS (pos), row, DEFAULT_FACE_ID);
@@ -10403,11 +10436,16 @@ include the height of both, if present, in the return 
value.  */)
   /* Subtract height of header-line which was counted automatically by
      start_display.  */
   y = it.current_y + it.max_ascent + it.max_descent
-    - WINDOW_HEADER_LINE_HEIGHT (w);
+    - WINDOW_TAB_LINE_HEIGHT (w) - WINDOW_HEADER_LINE_HEIGHT (w);
   /* Don't return more than Y-LIMIT.  */
   if (y > max_y)
     y = max_y;
 
+  if (EQ (mode_and_header_line, Qtab_line)
+      || EQ (mode_and_header_line, Qt))
+    /* Re-add height of tab-line as requested.  */
+    y = y + WINDOW_TAB_LINE_HEIGHT (w);
+
   if (EQ (mode_and_header_line, Qheader_line)
       || EQ (mode_and_header_line, Qt))
     /* Re-add height of header-line as requested.  */
@@ -12354,6 +12392,7 @@ prepare_menu_bars (void)
 
          menu_bar_hooks_run = update_menu_bar (f, false, menu_bar_hooks_run);
 #ifdef HAVE_WINDOW_SYSTEM
+         update_tab_bar (f, false);
          update_tool_bar (f, false);
 #endif
        }
@@ -12362,144 +12401,880 @@ prepare_menu_bars (void)
     }
   else
     {
-      struct frame *sf = SELECTED_FRAME ();
-      update_menu_bar (sf, true, false);
-#ifdef HAVE_WINDOW_SYSTEM
-      update_tool_bar (sf, true);
-#endif
-    }
-}
+      struct frame *sf = SELECTED_FRAME ();
+      update_menu_bar (sf, true, false);
+#ifdef HAVE_WINDOW_SYSTEM
+      update_tab_bar (sf, true);
+      update_tool_bar (sf, true);
+#endif
+    }
+}
+
+
+/* Update the menu bar item list for frame F.  This has to be done
+   before we start to fill in any display lines, because it can call
+   eval.
+
+   If SAVE_MATCH_DATA, we must save and restore it here.
+
+   If HOOKS_RUN, a previous call to update_menu_bar
+   already ran the menu bar hooks for this redisplay, so there
+   is no need to run them again.  The return value is the
+   updated value of this flag, to pass to the next call.  */
+
+static bool
+update_menu_bar (struct frame *f, bool save_match_data, bool hooks_run)
+{
+  Lisp_Object window;
+  struct window *w;
+
+  /* If called recursively during a menu update, do nothing.  This can
+     happen when, for instance, an activate-menubar-hook causes a
+     redisplay.  */
+  if (inhibit_menubar_update)
+    return hooks_run;
+
+  window = FRAME_SELECTED_WINDOW (f);
+  w = XWINDOW (window);
+
+  if (FRAME_WINDOW_P (f)
+      ?
+#ifdef HAVE_EXT_MENU_BAR
+      FRAME_EXTERNAL_MENU_BAR (f)
+#else
+      FRAME_MENU_BAR_LINES (f) > 0
+#endif
+      : FRAME_MENU_BAR_LINES (f) > 0)
+    {
+      /* If the user has switched buffers or windows, we need to
+        recompute to reflect the new bindings.  But we'll
+        recompute when update_mode_lines is set too; that means
+        that people can use force-mode-line-update to request
+        that the menu bar be recomputed.  The adverse effect on
+        the rest of the redisplay algorithm is about the same as
+        windows_or_buffers_changed anyway.  */
+      if (windows_or_buffers_changed
+         /* This used to test w->update_mode_line, but we believe
+            there is no need to recompute the menu in that case.  */
+         || update_mode_lines
+         || window_buffer_changed (w))
+       {
+         struct buffer *prev = current_buffer;
+         ptrdiff_t count = SPECPDL_INDEX ();
+
+         specbind (Qinhibit_menubar_update, Qt);
+
+         set_buffer_internal_1 (XBUFFER (w->contents));
+         if (save_match_data)
+           record_unwind_save_match_data ();
+         if (NILP (Voverriding_local_map_menu_flag))
+           {
+             specbind (Qoverriding_terminal_local_map, Qnil);
+             specbind (Qoverriding_local_map, Qnil);
+           }
+
+         if (!hooks_run)
+           {
+             /* Run the Lucid hook.  */
+             safe_run_hooks (Qactivate_menubar_hook);
+
+             /* If it has changed current-menubar from previous value,
+                really recompute the menu-bar from the value.  */
+             if (! NILP (Vlucid_menu_bar_dirty_flag))
+               call0 (Qrecompute_lucid_menubar);
+
+             safe_run_hooks (Qmenu_bar_update_hook);
+
+             hooks_run = true;
+           }
+
+         XSETFRAME (Vmenu_updating_frame, f);
+         fset_menu_bar_items (f, menu_bar_items (FRAME_MENU_BAR_ITEMS (f)));
+
+         /* Redisplay the menu bar in case we changed it.  */
+#ifdef HAVE_EXT_MENU_BAR
+         if (FRAME_WINDOW_P (f))
+            {
+#if defined (HAVE_NS)
+              /* All frames on Mac OS share the same menubar.  So only
+                 the selected frame should be allowed to set it.  */
+              if (f == SELECTED_FRAME ())
+#endif
+               set_frame_menubar (f, false, false);
+           }
+         else
+           /* On a terminal screen, the menu bar is an ordinary screen
+              line, and this makes it get updated.  */
+           w->update_mode_line = true;
+#else /* ! (HAVE_EXT_MENU_BAR) */
+         /* In the non-toolkit version, the menu bar is an ordinary screen
+            line, and this makes it get updated.  */
+         w->update_mode_line = true;
+#endif /* HAVE_EXT_MENU_BAR */
+
+         unbind_to (count, Qnil);
+         set_buffer_internal_1 (prev);
+       }
+    }
+
+  return hooks_run;
+}
+
+
+
+/***********************************************************************
+                              Tab-bars
+ ***********************************************************************/
+
+#ifdef HAVE_WINDOW_SYSTEM
+
+/* Select `frame' temporarily without running all the code in
+   do_switch_frame.
+   FIXME: Maybe do_switch_frame should be trimmed down similarly
+   when `norecord' is set.  */
+static void
+fast_set_selected_frame (Lisp_Object frame)
+{
+  if (!EQ (selected_frame, frame))
+    {
+      selected_frame = frame;
+      selected_window = XFRAME (frame)->selected_window;
+    }
+}
+
+/* Update the tab-bar item list for frame F.  This has to be done
+   before we start to fill in any display lines.  Called from
+   prepare_menu_bars.  If SAVE_MATCH_DATA, we must save
+   and restore it here.  */
+
+static void
+update_tab_bar (struct frame *f, bool save_match_data)
+{
+  bool do_update = (WINDOWP (f->tab_bar_window)
+                   && WINDOW_TOTAL_LINES (XWINDOW (f->tab_bar_window)) > 0);
+
+  if (do_update)
+    {
+      Lisp_Object window;
+      struct window *w;
+
+      window = FRAME_SELECTED_WINDOW (f);
+      w = XWINDOW (window);
+
+      /* If the user has switched buffers or windows, we need to
+        recompute to reflect the new bindings.  But we'll
+        recompute when update_mode_lines is set too; that means
+        that people can use force-mode-line-update to request
+        that the menu bar be recomputed.  The adverse effect on
+        the rest of the redisplay algorithm is about the same as
+        windows_or_buffers_changed anyway.  */
+      if (windows_or_buffers_changed
+         || w->update_mode_line
+         || update_mode_lines
+         || window_buffer_changed (w))
+       {
+         struct buffer *prev = current_buffer;
+         ptrdiff_t count = SPECPDL_INDEX ();
+         Lisp_Object frame, new_tab_bar;
+          int new_n_tab_bar;
+
+         /* Set current_buffer to the buffer of the selected
+            window of the frame, so that we get the right local
+            keymaps.  */
+         set_buffer_internal_1 (XBUFFER (w->contents));
+
+         /* Save match data, if we must.  */
+         if (save_match_data)
+           record_unwind_save_match_data ();
+
+         /* Make sure that we don't accidentally use bogus keymaps.  */
+         if (NILP (Voverriding_local_map_menu_flag))
+           {
+             specbind (Qoverriding_terminal_local_map, Qnil);
+             specbind (Qoverriding_local_map, Qnil);
+           }
+
+         /* We must temporarily set the selected frame to this frame
+            before calling tab_bar_items, because the calculation of
+            the tab-bar keymap uses the selected frame (see
+            `tab-bar-make-keymap' in tab-bar.el).  */
+         eassert (EQ (selected_window,
+                      /* Since we only explicitly preserve selected_frame,
+                         check that selected_window would be redundant.  */
+                      XFRAME (selected_frame)->selected_window));
+         record_unwind_protect (fast_set_selected_frame, selected_frame);
+         XSETFRAME (frame, f);
+         fast_set_selected_frame (frame);
+
+         /* Build desired tab-bar items from keymaps.  */
+          new_tab_bar
+           = tab_bar_items (Fcopy_sequence (f->tab_bar_items),
+                             &new_n_tab_bar);
+
+         /* Redisplay the tab-bar if we changed it.  */
+         if (new_n_tab_bar != f->n_tab_bar_items
+             || NILP (Fequal (new_tab_bar, f->tab_bar_items)))
+            {
+              /* Redisplay that happens asynchronously due to an expose event
+                 may access f->tab_bar_items.  Make sure we update both
+                 variables within BLOCK_INPUT so no such event interrupts.  */
+              block_input ();
+              fset_tab_bar_items (f, new_tab_bar);
+              f->n_tab_bar_items = new_n_tab_bar;
+              w->update_mode_line = true;
+              unblock_input ();
+            }
+
+         unbind_to (count, Qnil);
+         set_buffer_internal_1 (prev);
+       }
+    }
+}
+
+/* Set F->desired_tab_bar_string to a Lisp string representing frame
+   F's desired tab-bar contents.  F->tab_bar_items must have
+   been set up previously by calling prepare_menu_bars.  */
+
+static void
+build_desired_tab_bar_string (struct frame *f)
+{
+  int i;
+  Lisp_Object caption;
+
+  caption = Qnil;
+
+  /* Prepare F->desired_tab_bar_string.  Make a new string.  */
+  fset_desired_tab_bar_string (f, build_string (" "));
+
+  /* Put a `display' property on the string for the captions to display,
+     put a `menu_item' property on tab-bar items with a value that
+     is the index of the item in F's tab-bar item vector.  */
+  for (i = 0; i < f->n_tab_bar_items; ++i)
+    {
+#define PROP(IDX) \
+  AREF (f->tab_bar_items, i * TAB_BAR_ITEM_NSLOTS + (IDX))
+
+      caption = Fcopy_sequence (PROP (TAB_BAR_ITEM_CAPTION));
+
+      /* Put a `display' text property on the string for the caption to
+        display.  Put a `menu-item' property on the string that gives
+        the start of this item's properties in the tab-bar items
+        vector.  */
+      AUTO_LIST2 (props, Qmenu_item, make_fixnum (i * TAB_BAR_ITEM_NSLOTS));
+
+      Fadd_text_properties (make_fixnum (0), make_fixnum (SCHARS (caption)),
+                           props, caption);
+
+      f->desired_tab_bar_string =
+       concat2 (f->desired_tab_bar_string, caption);
+
+#undef PROP
+    }
+}
+
+
+/* Display one line of the tab-bar of frame IT->f.
+
+   HEIGHT specifies the desired height of the tab-bar line.
+   If the actual height of the glyph row is less than HEIGHT, the
+   row's height is increased to HEIGHT, and the icons are centered
+   vertically in the new height.
+
+   If HEIGHT is -1, we are counting needed tab-bar lines, so don't
+   count a final empty row in case the tab-bar width exactly matches
+   the window width.
+*/
+
+static void
+display_tab_bar_line (struct it *it, int height)
+{
+  struct glyph_row *row = it->glyph_row;
+  int max_x = it->last_visible_x;
+  struct glyph *last;
+
+  /* Don't extend on a previously drawn tab bar items (Bug#16058).  */
+  clear_glyph_row (row);
+  row->enabled_p = true;
+  row->y = it->current_y;
+
+  /* Note that this isn't made use of if the face hasn't a box,
+     so there's no need to check the face here.  */
+  it->start_of_box_run_p = true;
+
+  while (it->current_x < max_x)
+    {
+      int x, n_glyphs_before, i, nglyphs;
+      struct it it_before;
+
+      /* Get the next display element.  */
+      if (!get_next_display_element (it))
+       {
+         /* Don't count empty row if we are counting needed tab-bar lines.  */
+         if (height < 0 && !it->hpos)
+           return;
+         break;
+       }
+
+      /* Produce glyphs.  */
+      n_glyphs_before = row->used[TEXT_AREA];
+      it_before = *it;
+
+      PRODUCE_GLYPHS (it);
+
+      nglyphs = row->used[TEXT_AREA] - n_glyphs_before;
+      i = 0;
+      x = it_before.current_x;
+      while (i < nglyphs)
+       {
+         struct glyph *glyph = row->glyphs[TEXT_AREA] + n_glyphs_before + i;
+
+         if (x + glyph->pixel_width > max_x)
+           {
+             /* Glyph doesn't fit on line.  Backtrack.  */
+             row->used[TEXT_AREA] = n_glyphs_before;
+             *it = it_before;
+             /* If this is the only glyph on this line, it will never fit on 
the
+                tab-bar, so skip it.  But ensure there is at least one glyph,
+                so we don't accidentally disable the tab-bar.  */
+             if (n_glyphs_before == 0
+                 && (it->vpos > 0 || IT_STRING_CHARPOS (*it) < 
it->end_charpos-1))
+               break;
+             goto out;
+           }
+
+         ++it->hpos;
+         x += glyph->pixel_width;
+         ++i;
+       }
+
+      /* Stop at line end.  */
+      if (ITERATOR_AT_END_OF_LINE_P (it))
+       break;
+
+      set_iterator_to_next (it, true);
+    }
+
+ out:;
+
+  row->displays_text_p = row->used[TEXT_AREA] != 0;
+
+  /* Use default face for the border below the tab bar.
+
+     FIXME: When auto-resize-tab-bars is grow-only, there is
+     no additional border below the possibly empty tab-bar lines.
+     So to make the extra empty lines look "normal", we have to
+     use the tab-bar face for the border too.  */
+  if (!MATRIX_ROW_DISPLAYS_TEXT_P (row)
+      && !EQ (Vauto_resize_tab_bars, Qgrow_only))
+    it->face_id = DEFAULT_FACE_ID;
+
+  extend_face_to_end_of_line (it);
+  last = row->glyphs[TEXT_AREA] + row->used[TEXT_AREA] - 1;
+  last->right_box_line_p = true;
+  if (last == row->glyphs[TEXT_AREA])
+    last->left_box_line_p = true;
+
+  /* Make line the desired height and center it vertically.  */
+  if ((height -= it->max_ascent + it->max_descent) > 0)
+    {
+      /* Don't add more than one line height.  */
+      height %= FRAME_LINE_HEIGHT (it->f);
+      it->max_ascent += height / 2;
+      it->max_descent += (height + 1) / 2;
+    }
+
+  compute_line_metrics (it);
+
+  /* If line is empty, make it occupy the rest of the tab-bar.  */
+  if (!MATRIX_ROW_DISPLAYS_TEXT_P (row))
+    {
+      row->height = row->phys_height = it->last_visible_y - row->y;
+      row->visible_height = row->height;
+      row->ascent = row->phys_ascent = 0;
+      row->extra_line_spacing = 0;
+    }
+
+  row->full_width_p = true;
+  row->continued_p = false;
+  row->truncated_on_left_p = false;
+  row->truncated_on_right_p = false;
+
+  it->current_x = it->hpos = 0;
+  it->current_y += row->height;
+  ++it->vpos;
+  ++it->glyph_row;
+}
+
+
+/* Value is the number of pixels needed to make all tab-bar items of
+   frame F visible.  The actual number of glyph rows needed is
+   returned in *N_ROWS if non-NULL.  */
+static int
+tab_bar_height (struct frame *f, int *n_rows, bool pixelwise)
+{
+  struct window *w = XWINDOW (f->tab_bar_window);
+  struct it it;
+  /* tab_bar_height is called from redisplay_tab_bar after building
+     the desired matrix, so use (unused) mode-line row as temporary row to
+     avoid destroying the first tab-bar row.  */
+  struct glyph_row *temp_row = MATRIX_MODE_LINE_ROW (w->desired_matrix);
+
+  /* Initialize an iterator for iteration over
+     F->desired_tab_bar_string in the tab-bar window of frame F.  */
+  init_iterator (&it, w, -1, -1, temp_row, TAB_BAR_FACE_ID);
+  temp_row->reversed_p = false;
+  it.first_visible_x = 0;
+  it.last_visible_x = WINDOW_PIXEL_WIDTH (w);
+  reseat_to_string (&it, NULL, f->desired_tab_bar_string, 0, 0, 0, -1);
+  it.paragraph_embedding = L2R;
+
+  while (!ITERATOR_AT_END_P (&it))
+    {
+      clear_glyph_row (temp_row);
+      it.glyph_row = temp_row;
+      display_tab_bar_line (&it, -1);
+    }
+  clear_glyph_row (temp_row);
+
+  /* f->n_tab_bar_rows == 0 means "unknown"; -1 means no tab-bar.  */
+  if (n_rows)
+    *n_rows = it.vpos > 0 ? it.vpos : -1;
+
+  if (pixelwise)
+    return it.current_y;
+  else
+    return (it.current_y + FRAME_LINE_HEIGHT (f) - 1) / FRAME_LINE_HEIGHT (f);
+}
+
+DEFUN ("tab-bar-height", Ftab_bar_height, Stab_bar_height,
+       0, 2, 0,
+       doc: /* Return the number of lines occupied by the tab bar of FRAME.
+If FRAME is nil or omitted, use the selected frame.  Optional argument
+PIXELWISE non-nil means return the height of the tab bar in pixels.  */)
+  (Lisp_Object frame, Lisp_Object pixelwise)
+{
+  int height = 0;
+
+  struct frame *f = decode_any_frame (frame);
+
+  if (WINDOWP (f->tab_bar_window)
+      && WINDOW_PIXEL_HEIGHT (XWINDOW (f->tab_bar_window)) > 0)
+    {
+      update_tab_bar (f, true);
+      if (f->n_tab_bar_items)
+       {
+         build_desired_tab_bar_string (f);
+         height = tab_bar_height (f, NULL, !NILP (pixelwise));
+       }
+    }
+
+  return make_fixnum (height);
+}
+
+
+/* Display the tab-bar of frame F.  Value is true if tab-bar's
+   height should be changed.  */
+static bool
+redisplay_tab_bar (struct frame *f)
+{
+  f->tab_bar_redisplayed = true;
+
+  struct window *w;
+  struct it it;
+  struct glyph_row *row;
+
+  /* If frame hasn't a tab-bar window or if it is zero-height, don't
+     do anything.  This means you must start with tab-bar-lines
+     non-zero to get the auto-sizing effect.  Or in other words, you
+     can turn off tab-bars by specifying tab-bar-lines zero.  */
+  if (!WINDOWP (f->tab_bar_window)
+      || (w = XWINDOW (f->tab_bar_window),
+          WINDOW_TOTAL_LINES (w) == 0))
+    return false;
+
+  /* Set up an iterator for the tab-bar window.  */
+  init_iterator (&it, w, -1, -1, w->desired_matrix->rows, TAB_BAR_FACE_ID);
+  it.first_visible_x = 0;
+  it.last_visible_x = WINDOW_PIXEL_WIDTH (w);
+  row = it.glyph_row;
+  row->reversed_p = false;
+
+  /* Build a string that represents the contents of the tab-bar.  */
+  build_desired_tab_bar_string (f);
+  reseat_to_string (&it, NULL, f->desired_tab_bar_string, 0, 0, 0, -1);
+  /* FIXME: This should be controlled by a user option.  But it
+     doesn't make sense to have an R2L tab bar if the menu bar cannot
+     be drawn also R2L, and making the menu bar R2L is tricky due
+     tabkit-specific code that implements it.  If an R2L tab bar is
+     ever supported, display_tab_bar_line should also be augmented to
+     call unproduce_glyphs like display_line and display_string
+     do.  */
+  it.paragraph_embedding = L2R;
+
+  if (f->n_tab_bar_rows == 0)
+    {
+      int new_height = tab_bar_height (f, &f->n_tab_bar_rows, true);
+
+      if (new_height != WINDOW_PIXEL_HEIGHT (w))
+       {
+          if (FRAME_TERMINAL (f)->change_tab_bar_height_hook)
+            FRAME_TERMINAL (f)->change_tab_bar_height_hook (f, new_height);
+         frame_default_tab_bar_height = new_height;
+         /* Always do that now.  */
+         clear_glyph_matrix (w->desired_matrix);
+         f->fonts_changed = true;
+         return true;
+       }
+    }
+
+  /* Display as many lines as needed to display all tab-bar items.  */
+
+  if (f->n_tab_bar_rows > 0)
+    {
+      int border, rows, height, extra;
+
+      if (TYPE_RANGED_FIXNUMP (int, Vtab_bar_border))
+       border = XFIXNUM (Vtab_bar_border);
+      else if (EQ (Vtab_bar_border, Qinternal_border_width))
+       border = FRAME_INTERNAL_BORDER_WIDTH (f);
+      else if (EQ (Vtab_bar_border, Qborder_width))
+       border = f->border_width;
+      else
+       border = 0;
+      if (border < 0)
+       border = 0;
+
+      rows = f->n_tab_bar_rows;
+      height = max (1, (it.last_visible_y - border) / rows);
+      extra = it.last_visible_y - border - height * rows;
+
+      while (it.current_y < it.last_visible_y)
+       {
+         int h = 0;
+         if (extra > 0 && rows-- > 0)
+           {
+             h = (extra + rows - 1) / rows;
+             extra -= h;
+           }
+         display_tab_bar_line (&it, height + h);
+       }
+    }
+  else
+    {
+      while (it.current_y < it.last_visible_y)
+       display_tab_bar_line (&it, 0);
+    }
+
+  /* It doesn't make much sense to try scrolling in the tab-bar
+     window, so don't do it.  */
+  w->desired_matrix->no_scrolling_p = true;
+  w->must_be_updated_p = true;
+
+  if (!NILP (Vauto_resize_tab_bars))
+    {
+      bool change_height_p = true;
+
+      /* If we couldn't display everything, change the tab-bar's
+        height if there is room for more.  */
+      if (IT_STRING_CHARPOS (it) < it.end_charpos)
+       change_height_p = true;
+
+      /* We subtract 1 because display_tab_bar_line advances the
+        glyph_row pointer before returning to its caller.  We want to
+        examine the last glyph row produced by
+        display_tab_bar_line.  */
+      row = it.glyph_row - 1;
+
+      /* If there are blank lines at the end, except for a partially
+        visible blank line at the end that is smaller than
+        FRAME_LINE_HEIGHT, change the tab-bar's height.  */
+      if (!MATRIX_ROW_DISPLAYS_TEXT_P (row)
+         && row->height >= FRAME_LINE_HEIGHT (f))
+       change_height_p = true;
+
+      /* If row displays tab-bar items, but is partially visible,
+        change the tab-bar's height.  */
+      if (MATRIX_ROW_DISPLAYS_TEXT_P (row)
+         && MATRIX_ROW_BOTTOM_Y (row) > it.last_visible_y)
+       change_height_p = true;
+
+      /* Resize windows as needed by changing the `tab-bar-lines'
+        frame parameter.  */
+      if (change_height_p)
+       {
+         int nrows;
+         int new_height = tab_bar_height (f, &nrows, true);
+
+         change_height_p = ((EQ (Vauto_resize_tab_bars, Qgrow_only)
+                             && !f->minimize_tab_bar_window_p)
+                            ? (new_height > WINDOW_PIXEL_HEIGHT (w))
+                            : (new_height != WINDOW_PIXEL_HEIGHT (w)));
+         f->minimize_tab_bar_window_p = false;
+
+         if (change_height_p)
+           {
+              if (FRAME_TERMINAL (f)->change_tab_bar_height_hook)
+                FRAME_TERMINAL (f)->change_tab_bar_height_hook (f, new_height);
+             frame_default_tab_bar_height = new_height;
+             clear_glyph_matrix (w->desired_matrix);
+             f->n_tab_bar_rows = nrows;
+             f->fonts_changed = true;
+
+             return true;
+           }
+       }
+    }
+
+  f->minimize_tab_bar_window_p = false;
+  return false;
+}
+
+/* Get information about the tab-bar item which is displayed in GLYPH
+   on frame F.  Return in *PROP_IDX the index where tab-bar item
+   properties start in F->tab_bar_items.  Value is false if
+   GLYPH doesn't display a tab-bar item.  */
+
+static bool
+tab_bar_item_info (struct frame *f, struct glyph *glyph, int *prop_idx)
+{
+  Lisp_Object prop;
+  int charpos;
+
+  /* This function can be called asynchronously, which means we must
+     exclude any possibility that Fget_text_property signals an
+     error.  */
+  charpos = min (SCHARS (f->current_tab_bar_string), glyph->charpos);
+  charpos = max (0, charpos);
+
+  /* Get the text property `menu-item' at pos. The value of that
+     property is the start index of this item's properties in
+     F->tab_bar_items.  */
+  prop = Fget_text_property (make_fixnum (charpos),
+                            Qmenu_item, f->current_tab_bar_string);
+  if (! FIXNUMP (prop))
+    return false;
+  *prop_idx = XFIXNUM (prop);
+  return true;
+}
+
+
+/* Get information about the tab-bar item at position X/Y on frame F.
+   Return in *GLYPH a pointer to the glyph of the tab-bar item in
+   the current matrix of the tab-bar window of F, or NULL if not
+   on a tab-bar item.  Return in *PROP_IDX the index of the tab-bar
+   item in F->tab_bar_items.  Value is
+
+   -1  if X/Y is not on a tab-bar item
+   0   if X/Y is on the same item that was highlighted before.
+   1   otherwise.  */
+
+static int
+get_tab_bar_item (struct frame *f, int x, int y, struct glyph **glyph,
+                  int *hpos, int *vpos, int *prop_idx)
+{
+  Mouse_HLInfo *hlinfo = MOUSE_HL_INFO (f);
+  struct window *w = XWINDOW (f->tab_bar_window);
+  int area;
+
+  /* Find the glyph under X/Y.  */
+  *glyph = x_y_to_hpos_vpos (w, x, y, hpos, vpos, 0, 0, &area);
+  if (*glyph == NULL)
+    return -1;
+
+  /* Get the start of this tab-bar item's properties in
+     f->tab_bar_items.  */
+  if (!tab_bar_item_info (f, *glyph, prop_idx))
+    return -1;
+
+  /* Is mouse on the highlighted item?  */
+  if (EQ (f->tab_bar_window, hlinfo->mouse_face_window)
+      && *vpos >= hlinfo->mouse_face_beg_row
+      && *vpos <= hlinfo->mouse_face_end_row
+      && (*vpos > hlinfo->mouse_face_beg_row
+         || *hpos >= hlinfo->mouse_face_beg_col)
+      && (*vpos < hlinfo->mouse_face_end_row
+         || *hpos < hlinfo->mouse_face_end_col
+         || hlinfo->mouse_face_past_end))
+    return 0;
+
+  return 1;
+}
+
+
+/* EXPORT:
+   Handle mouse button event on the tab-bar of frame F, at
+   frame-relative coordinates X/Y.  DOWN_P is true for a button press,
+   false for button release.  MODIFIERS is event modifiers for button
+   release.  */
+
+void
+handle_tab_bar_click (struct frame *f, int x, int y, bool down_p,
+                      int modifiers)
+{
+  Mouse_HLInfo *hlinfo = MOUSE_HL_INFO (f);
+  struct window *w = XWINDOW (f->tab_bar_window);
+  int hpos, vpos, prop_idx;
+  struct glyph *glyph;
+  Lisp_Object enabled_p;
+  int ts;
+
+  /* If not on the highlighted tab-bar item, and mouse-highlight is
+     non-nil, return.  This is so we generate the tab-bar button
+     click only when the mouse button is released on the same item as
+     where it was pressed.  However, when mouse-highlight is disabled,
+     generate the click when the button is released regardless of the
+     highlight, since tab-bar items are not highlighted in that
+     case.  */
+  frame_to_window_pixel_xy (w, &x, &y);
+  ts = get_tab_bar_item (f, x, y, &glyph, &hpos, &vpos, &prop_idx);
+  if (ts == -1
+      || (ts != 0 && !NILP (Vmouse_highlight)))
+    return;
+
+  /* When mouse-highlight is off, generate the click for the item
+     where the button was pressed, disregarding where it was
+     released.  */
+  if (NILP (Vmouse_highlight) && !down_p)
+    prop_idx = f->last_tab_bar_item;
+
+  /* If item is disabled, do nothing.  */
+  enabled_p = AREF (f->tab_bar_items, prop_idx + TAB_BAR_ITEM_ENABLED_P);
+  if (NILP (enabled_p))
+    return;
+
+  if (down_p)
+    {
+      /* Show item in pressed state.  */
+      if (!NILP (Vmouse_highlight))
+       show_mouse_face (hlinfo, DRAW_IMAGE_SUNKEN);
+      f->last_tab_bar_item = prop_idx;
+    }
+  else
+    {
+      Lisp_Object key, frame;
+      struct input_event event;
+      EVENT_INIT (event);
 
+      /* Show item in released state.  */
+      if (!NILP (Vmouse_highlight))
+       show_mouse_face (hlinfo, DRAW_IMAGE_RAISED);
 
-/* Update the menu bar item list for frame F.  This has to be done
-   before we start to fill in any display lines, because it can call
-   eval.
+      key = AREF (f->tab_bar_items, prop_idx + TAB_BAR_ITEM_KEY);
 
-   If SAVE_MATCH_DATA, we must save and restore it here.
+      XSETFRAME (frame, f);
+      event.kind = TAB_BAR_EVENT;
+      event.frame_or_window = frame;
+      event.arg = frame;
+      kbd_buffer_store_event (&event);
 
-   If HOOKS_RUN, a previous call to update_menu_bar
-   already ran the menu bar hooks for this redisplay, so there
-   is no need to run them again.  The return value is the
-   updated value of this flag, to pass to the next call.  */
+      event.kind = TAB_BAR_EVENT;
+      event.frame_or_window = frame;
+      event.arg = key;
+      event.modifiers = modifiers;
+      kbd_buffer_store_event (&event);
+      f->last_tab_bar_item = -1;
+    }
+}
 
-static bool
-update_menu_bar (struct frame *f, bool save_match_data, bool hooks_run)
-{
-  Lisp_Object window;
-  struct window *w;
 
-  /* If called recursively during a menu update, do nothing.  This can
-     happen when, for instance, an activate-menubar-hook causes a
-     redisplay.  */
-  if (inhibit_menubar_update)
-    return hooks_run;
+/* Possibly highlight a tab-bar item on frame F when mouse moves to
+   tab-bar window-relative coordinates X/Y.  Called from
+   note_mouse_highlight.  */
 
-  window = FRAME_SELECTED_WINDOW (f);
-  w = XWINDOW (window);
+static void
+note_tab_bar_highlight (struct frame *f, int x, int y)
+{
+  Lisp_Object window = f->tab_bar_window;
+  struct window *w = XWINDOW (window);
+  Display_Info *dpyinfo = FRAME_DISPLAY_INFO (f);
+  Mouse_HLInfo *hlinfo = MOUSE_HL_INFO (f);
+  int hpos, vpos;
+  struct glyph *glyph;
+  struct glyph_row *row;
+  int i;
+  Lisp_Object enabled_p;
+  int prop_idx;
+  enum draw_glyphs_face draw = DRAW_IMAGE_RAISED;
+  bool mouse_down_p;
+  int rc;
 
-  if (FRAME_WINDOW_P (f)
-      ?
-#ifdef HAVE_EXT_MENU_BAR
-      FRAME_EXTERNAL_MENU_BAR (f)
-#else
-      FRAME_MENU_BAR_LINES (f) > 0
-#endif
-      : FRAME_MENU_BAR_LINES (f) > 0)
+  /* Function note_mouse_highlight is called with negative X/Y
+     values when mouse moves outside of the frame.  */
+  if (x <= 0 || y <= 0)
     {
-      /* If the user has switched buffers or windows, we need to
-        recompute to reflect the new bindings.  But we'll
-        recompute when update_mode_lines is set too; that means
-        that people can use force-mode-line-update to request
-        that the menu bar be recomputed.  The adverse effect on
-        the rest of the redisplay algorithm is about the same as
-        windows_or_buffers_changed anyway.  */
-      if (windows_or_buffers_changed
-         /* This used to test w->update_mode_line, but we believe
-            there is no need to recompute the menu in that case.  */
-         || update_mode_lines
-         || window_buffer_changed (w))
-       {
-         struct buffer *prev = current_buffer;
-         ptrdiff_t count = SPECPDL_INDEX ();
+      clear_mouse_face (hlinfo);
+      return;
+    }
 
-         specbind (Qinhibit_menubar_update, Qt);
+  rc = get_tab_bar_item (f, x, y, &glyph, &hpos, &vpos, &prop_idx);
+  if (rc < 0)
+    {
+      /* Not on tab-bar item.  */
+      clear_mouse_face (hlinfo);
+      return;
+    }
+  else if (rc == 0)
+    /* On same tab-bar item as before.  */
+    goto set_help_echo;
 
-         set_buffer_internal_1 (XBUFFER (w->contents));
-         if (save_match_data)
-           record_unwind_save_match_data ();
-         if (NILP (Voverriding_local_map_menu_flag))
-           {
-             specbind (Qoverriding_terminal_local_map, Qnil);
-             specbind (Qoverriding_local_map, Qnil);
-           }
+  clear_mouse_face (hlinfo);
 
-         if (!hooks_run)
-           {
-             /* Run the Lucid hook.  */
-             safe_run_hooks (Qactivate_menubar_hook);
+  /* Mouse is down, but on different tab-bar item?  */
+  mouse_down_p = (gui_mouse_grabbed (dpyinfo)
+                 && f == dpyinfo->last_mouse_frame);
 
-             /* If it has changed current-menubar from previous value,
-                really recompute the menu-bar from the value.  */
-             if (! NILP (Vlucid_menu_bar_dirty_flag))
-               call0 (Qrecompute_lucid_menubar);
+  if (mouse_down_p && f->last_tab_bar_item != prop_idx)
+    return;
 
-             safe_run_hooks (Qmenu_bar_update_hook);
+  draw = mouse_down_p ? DRAW_IMAGE_SUNKEN : DRAW_IMAGE_RAISED;
 
-             hooks_run = true;
-           }
+  /* If tab-bar item is not enabled, don't highlight it.  */
+  enabled_p = AREF (f->tab_bar_items, prop_idx + TAB_BAR_ITEM_ENABLED_P);
+  if (!NILP (enabled_p) && !NILP (Vmouse_highlight))
+    {
+      /* Compute the x-position of the glyph.  In front and past the
+        image is a space.  We include this in the highlighted area.  */
+      row = MATRIX_ROW (w->current_matrix, vpos);
+      for (i = x = 0; i < hpos; ++i)
+       x += row->glyphs[TEXT_AREA][i].pixel_width;
 
-         XSETFRAME (Vmenu_updating_frame, f);
-         fset_menu_bar_items (f, menu_bar_items (FRAME_MENU_BAR_ITEMS (f)));
+      /* Record this as the current active region.  */
+      hlinfo->mouse_face_beg_col = hpos;
+      hlinfo->mouse_face_beg_row = vpos;
+      hlinfo->mouse_face_beg_x = x;
+      hlinfo->mouse_face_past_end = false;
 
-         /* Redisplay the menu bar in case we changed it.  */
-#ifdef HAVE_EXT_MENU_BAR
-         if (FRAME_WINDOW_P (f))
-            {
-#if defined (HAVE_NS)
-              /* All frames on Mac OS share the same menubar.  So only
-                 the selected frame should be allowed to set it.  */
-              if (f == SELECTED_FRAME ())
-#endif
-               set_frame_menubar (f, false, false);
-           }
-         else
-           /* On a terminal screen, the menu bar is an ordinary screen
-              line, and this makes it get updated.  */
-           w->update_mode_line = true;
-#else /* ! (HAVE_EXT_MENU_BAR) */
-         /* In the non-toolkit version, the menu bar is an ordinary screen
-            line, and this makes it get updated.  */
-         w->update_mode_line = true;
-#endif /* HAVE_EXT_MENU_BAR */
+      hlinfo->mouse_face_end_col = hpos + 1;
+      hlinfo->mouse_face_end_row = vpos;
+      hlinfo->mouse_face_end_x = x + glyph->pixel_width;
+      hlinfo->mouse_face_window = window;
+      hlinfo->mouse_face_face_id = TAB_BAR_FACE_ID;
 
-         unbind_to (count, Qnil);
-         set_buffer_internal_1 (prev);
-       }
+      /* Display it as active.  */
+      show_mouse_face (hlinfo, draw);
     }
 
-  return hooks_run;
+ set_help_echo:
+
+  /* Set help_echo_string to a help string to display for this tab-bar item.
+     XTread_socket does the rest.  */
+  help_echo_object = help_echo_window = Qnil;
+  help_echo_pos = -1;
+  help_echo_string = AREF (f->tab_bar_items, prop_idx + TAB_BAR_ITEM_HELP);
+  if (NILP (help_echo_string))
+    help_echo_string = AREF (f->tab_bar_items, prop_idx + 
TAB_BAR_ITEM_CAPTION);
 }
 
+#endif /* HAVE_WINDOW_SYSTEM */
+
+
+
 /***********************************************************************
                               Tool-bars
  ***********************************************************************/
 
 #ifdef HAVE_WINDOW_SYSTEM
 
-/* Select `frame' temporarily without running all the code in
-   do_switch_frame.
-   FIXME: Maybe do_switch_frame should be trimmed down similarly
-   when `norecord' is set.  */
-static void
-fast_set_selected_frame (Lisp_Object frame)
-{
-  if (!EQ (selected_frame, frame))
-    {
-      selected_frame = frame;
-      selected_window = XFRAME (frame)->selected_window;
-    }
-}
-
 /* Update the tool-bar item list for frame F.  This has to be done
    before we start to fill in any display lines.  Called from
    prepare_menu_bars.  If SAVE_MATCH_DATA, we must save
@@ -16252,7 +17027,7 @@ compute_window_start_on_continuation_line (struct 
window *w)
 
       /* Find the start of the continued line.  This should be fast
         because find_newline is fast (newline cache).  */
-      row = w->desired_matrix->rows + window_wants_header_line (w);
+      row = w->desired_matrix->rows + window_wants_tab_line (w) + 
window_wants_header_line (w);
       init_iterator (&it, w, CHARPOS (start_pos), BYTEPOS (start_pos),
                     row, DEFAULT_FACE_ID);
       reseat_at_previous_visible_line_start (&it);
@@ -16415,6 +17190,8 @@ try_cursor_movement (Lisp_Object window, struct 
text_pos startp,
       this_scroll_margin = window_scroll_margin (w, MARGIN_IN_PIXELS);
 
       top_scroll_margin = this_scroll_margin;
+      if (window_wants_tab_line (w))
+       top_scroll_margin += CURRENT_TAB_LINE_HEIGHT (w);
       if (window_wants_header_line (w))
        top_scroll_margin += CURRENT_HEADER_LINE_HEIGHT (w);
 
@@ -17184,13 +17961,14 @@ redisplay_window (Lisp_Object window, bool 
just_this_one_p)
             margin, even though this part handles windows that didn't
             scroll at all.  */
           int pixel_margin = margin * frame_line_height;
+         bool tab_line = window_wants_tab_line (w);
          bool header_line = window_wants_header_line (w);
 
          /* Note: We add an extra FRAME_LINE_HEIGHT, because the loop
             below, which finds the row to move point to, advances by
             the Y coordinate of the _next_ row, see the definition of
             MATRIX_ROW_BOTTOM_Y.  */
-         if (w->cursor.vpos < margin + header_line)
+         if (w->cursor.vpos < margin + tab_line + header_line)
            {
              w->cursor.vpos = -1;
              clear_glyph_matrix (w->desired_matrix);
@@ -17200,6 +17978,8 @@ redisplay_window (Lisp_Object window, bool 
just_this_one_p)
            {
              int window_height = window_box_height (w);
 
+             if (tab_line)
+               window_height += CURRENT_TAB_LINE_HEIGHT (w);
              if (header_line)
                window_height += CURRENT_HEADER_LINE_HEIGHT (w);
              if (w->cursor.y >= window_height - pixel_margin)
@@ -17531,7 +18311,7 @@ redisplay_window (Lisp_Object window, bool 
just_this_one_p)
                centering_position -= pt_offset;
              centering_position -=
                (frame_line_height * (1 + margin + last_line_misfit)
-                + WINDOW_HEADER_LINE_HEIGHT (w));
+                + WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w));
              /* Don't let point enter the scroll margin near top of
                 the window.  */
              if (centering_position < margin * frame_line_height)
@@ -17759,7 +18539,8 @@ redisplay_window (Lisp_Object window, bool 
just_this_one_p)
           && (w->column_number_displayed != current_column ())))
       /* This means that the window has a mode line.  */
       && (window_wants_mode_line (w)
-         || window_wants_header_line (w)))
+         || window_wants_header_line (w)
+          || window_wants_tab_line (w)))
     {
 
       display_mode_lines (w);
@@ -17775,6 +18556,17 @@ redisplay_window (Lisp_Object window, bool 
just_this_one_p)
            = DESIRED_MODE_LINE_HEIGHT (w);
        }
 
+      /* If tab line height has changed, arrange for a thorough
+        immediate redisplay using the correct tab line height.  */
+      if (window_wants_tab_line (w)
+         && CURRENT_TAB_LINE_HEIGHT (w) != DESIRED_TAB_LINE_HEIGHT (w))
+       {
+         f->fonts_changed = true;
+         w->tab_line_height = -1;
+         MATRIX_TAB_LINE_ROW (w->current_matrix)->height
+           = DESIRED_TAB_LINE_HEIGHT (w);
+       }
+
       /* If header line height has changed, arrange for a thorough
         immediate redisplay using the correct header line height.  */
       if (window_wants_header_line (w)
@@ -17822,6 +18614,12 @@ redisplay_window (Lisp_Object window, bool 
just_this_one_p)
 #ifdef HAVE_WINDOW_SYSTEM
       if (FRAME_WINDOW_P (f))
         {
+         if (WINDOWP (f->tab_bar_window)
+             && (FRAME_TAB_BAR_LINES (f) > 0
+                 || !NILP (Vauto_resize_tab_bars))
+             && redisplay_tab_bar (f))
+           ignore_mouse_drag_p = true;
+
 #ifdef HAVE_EXT_TOOL_BAR
          if (FRAME_EXTERNAL_TOOL_BAR (f))
            redisplay_tool_bar (f);
@@ -18045,6 +18843,11 @@ try_window_reusing_current_matrix (struct window *w)
     return false;
 
   /* If top-line visibility has changed, give up.  */
+  if (window_wants_tab_line (w)
+      != MATRIX_TAB_LINE_ROW (w->current_matrix)->mode_line_p)
+    return false;
+
+  /* If top-line visibility has changed, give up.  */
   if (window_wants_header_line (w)
       != MATRIX_HEADER_LINE_ROW (w->current_matrix)->mode_line_p)
     return false;
@@ -18189,7 +18992,7 @@ try_window_reusing_current_matrix (struct window *w)
            (start_row + i)->enabled_p = false;
 
          /* Re-compute Y positions.  */
-         min_y = WINDOW_HEADER_LINE_HEIGHT (w);
+         min_y = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w);
          max_y = it.last_visible_y;
          for (row = start_row + nrows_scrolled;
               row < bottom_row;
@@ -18216,7 +19019,7 @@ try_window_reusing_current_matrix (struct window *w)
          /* Disable lines in the current matrix which are now
             below the window.  */
          for (++row; row < bottom_row; ++row)
-           row->enabled_p = row->mode_line_p = false;
+           row->enabled_p = row->mode_line_p = row->tab_line_p = false;
        }
 
       /* Update window_end_pos etc.; last_reused_text_row is the last
@@ -18294,7 +19097,7 @@ try_window_reusing_current_matrix (struct window *w)
       it.vpos = (MATRIX_ROW_VPOS (first_row_to_display, w->current_matrix)
                 - nrows_scrolled);
       it.current_y = (first_row_to_display->y - first_reusable_row->y
-                     + WINDOW_HEADER_LINE_HEIGHT (w));
+                     + WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT 
(w));
 
       /* Display lines beginning with first_row_to_display in the
          desired matrix.  Set last_text_row to the last row displayed
@@ -18327,7 +19130,7 @@ try_window_reusing_current_matrix (struct window *w)
 
       /* Scroll the display.  */
       run.current_y = first_reusable_row->y;
-      run.desired_y = WINDOW_HEADER_LINE_HEIGHT (w);
+      run.desired_y = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT 
(w);
       run.height = it.last_visible_y - run.current_y;
       dy = run.current_y - run.desired_y;
 
@@ -18345,7 +19148,7 @@ try_window_reusing_current_matrix (struct window *w)
 
       /* Adjust Y positions of reused rows.  */
       bottom_row = MATRIX_BOTTOM_TEXT_ROW (w->current_matrix, w);
-      min_y = WINDOW_HEADER_LINE_HEIGHT (w);
+      min_y = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w);
       max_y = it.last_visible_y;
       for (row = first_reusable_row; row < first_row_to_display; ++row)
        {
@@ -19303,6 +20106,7 @@ try_window_id (struct window *w)
            = MATRIX_ROW_VPOS (first_unchanged_at_end_row, w->current_matrix);
          int from = WINDOW_TOP_EDGE_LINE (w) + from_vpos;
          int end = (WINDOW_TOP_EDGE_LINE (w)
+                    + window_wants_tab_line (w)
                     + window_wants_header_line (w)
                     + window_internal_height (w));
 
@@ -19481,7 +20285,7 @@ try_window_id (struct window *w)
     {
       /* Displayed to end of window, but no line containing text was
         displayed.  Lines were deleted at the end of the window.  */
-      bool first_vpos = window_wants_header_line (w);
+      int first_vpos = window_wants_tab_line (w) + window_wants_header_line 
(w);
       int vpos = w->window_end_vpos;
       struct glyph_row *current_row = current_matrix->rows + vpos;
       struct glyph_row *desired_row = desired_matrix->rows + vpos;
@@ -19853,6 +20657,36 @@ GLYPHS > 1 or omitted means dump glyphs in long form.  
*/)
 }
 
 
+DEFUN ("dump-tab-bar-row", Fdump_tab_bar_row, Sdump_tab_bar_row, 1, 2, "P",
+       doc: /* Dump glyph row ROW of the tab-bar of the current frame to 
stderr.
+Interactively, ROW is the prefix numeric argument and defaults to zero.
+GLYPHS 0 means don't dump glyphs.
+GLYPHS 1 means dump glyphs in short form.
+GLYPHS > 1 or omitted means dump glyphs in long form.
+
+If there's no tab-bar, or if the tab-bar is not drawn by Emacs,
+do nothing.  */)
+  (Lisp_Object row, Lisp_Object glyphs)
+{
+#if defined (HAVE_WINDOW_SYSTEM)
+  struct frame *sf = SELECTED_FRAME ();
+  struct glyph_matrix *m = XWINDOW (sf->tab_bar_window)->current_matrix;
+  EMACS_INT vpos;
+
+  if (NILP (row))
+    vpos = 0;
+  else
+    {
+      CHECK_FIXNUM (row);
+      vpos = XFIXNUM (row);
+    }
+  if (vpos >= 0 && vpos < m->nrows)
+    dump_glyph_row (MATRIX_ROW (m, vpos), vpos,
+                   TYPE_RANGED_FIXNUMP (int, glyphs) ? XFIXNUM (glyphs) : 2);
+#endif
+  return Qnil;
+}
+
 DEFUN ("dump-tool-bar-row", Fdump_tool_bar_row, Sdump_tool_bar_row, 1, 2, "P",
        doc: /* Dump glyph row ROW of the tool-bar of the current frame to 
stderr.
 Interactively, ROW is the prefix numeric argument and defaults to zero.
@@ -20220,7 +21054,7 @@ compute_line_metrics (struct it *it)
       /* Compute how much of the line is visible.  */
       row->visible_height = row->height;
 
-      min_y = WINDOW_HEADER_LINE_HEIGHT (it->w);
+      min_y = WINDOW_TAB_LINE_HEIGHT (it->w) + WINDOW_HEADER_LINE_HEIGHT 
(it->w);
       max_y = WINDOW_BOX_HEIGHT_NO_MODE_LINE (it->w);
 
       if (row->y < min_y)
@@ -20534,6 +21368,8 @@ extend_face_to_end_of_line (struct it *it)
       /* Mode line and the header line don't have margins, and
         likewise the frame's tool-bar window, if there is any.  */
       if (!(it->glyph_row->mode_line_p
+           || (WINDOWP (f->tab_bar_window)
+               && it->w == XWINDOW (f->tab_bar_window))
 #ifndef HAVE_EXT_TOOL_BAR
            || (WINDOWP (f->tool_bar_window)
                && it->w == XWINDOW (f->tool_bar_window))
@@ -21730,9 +22566,10 @@ display_line (struct it *it, int cursor_vpos)
   ptrdiff_t min_pos = ZV + 1, max_pos = 0;
   ptrdiff_t min_bpos UNINIT, max_bpos UNINIT;
   bool pending_handle_line_prefix = false;
+  int tab_line = window_wants_tab_line (it->w);
   int header_line = window_wants_header_line (it->w);
   bool hscroll_this_line = (cursor_vpos >= 0
-                           && it->vpos == cursor_vpos - header_line
+                           && it->vpos == cursor_vpos - tab_line - header_line
                            && hscrolling_current_line_p (it->w));
   int first_visible_x = it->first_visible_x;
   int last_visible_x = it->last_visible_x;
@@ -23773,6 +24610,15 @@ display_mode_lines (struct window *w)
       ++n;
     }
 
+  if (window_wants_tab_line (w))
+    {
+      Lisp_Object window_tab_line_format
+       = window_parameter (w, Qtab_line_format);
+
+      display_mode_line (w, TAB_LINE_FACE_ID, window_tab_line_format);
+      ++n;
+    }
+
   if (window_wants_header_line (w))
     {
       Lisp_Object window_header_line_format
@@ -23794,10 +24640,10 @@ display_mode_lines (struct window *w)
 }
 
 
-/* Display mode or header line of window W.  FACE_ID specifies which
-   line to display; it is either MODE_LINE_FACE_ID or
-   HEADER_LINE_FACE_ID.  FORMAT is the mode/header line format to
-   display.  Value is the pixel height of the mode/header line
+/* Display mode or header/tab line of window W.  FACE_ID specifies which
+   line to display; it is either MODE_LINE_FACE_ID, HEADER_LINE_FACE_ID or
+   TAB_LINE_FACE_ID.  FORMAT is the mode/header/tab line format to
+   display.  Value is the pixel height of the mode/header/tab line
    displayed.  */
 
 static int
@@ -23814,6 +24660,8 @@ display_mode_line (struct window *w, enum face_id 
face_id, Lisp_Object format)
   prepare_desired_row (w, it.glyph_row, true);
 
   it.glyph_row->mode_line_p = true;
+  if (face_id == TAB_LINE_FACE_ID)
+    it.glyph_row->tab_line_p = true;
 
   /* FIXME: This should be controlled by a user option.  But
      supporting such an option is not trivial, since the mode line is
@@ -24531,6 +25379,8 @@ are the selected window and the WINDOW's buffer).  */)
     : EQ (face, Qmode_line) ? MODE_LINE_FACE_ID
     : EQ (face, Qmode_line_inactive) ? MODE_LINE_INACTIVE_FACE_ID
     : EQ (face, Qheader_line) ? HEADER_LINE_FACE_ID
+    : EQ (face, Qtab_line) ? TAB_LINE_FACE_ID
+    : EQ (face, Qtab_bar) ? TAB_BAR_FACE_ID
     : EQ (face, Qtool_bar) ? TOOL_BAR_FACE_ID
     : DEFAULT_FACE_ID;
 
@@ -29462,7 +30312,7 @@ gui_clear_end_of_line (struct window *w, struct 
glyph_row *updated_row,
       to_x += area_left;
     }
 
-  min_y = WINDOW_HEADER_LINE_HEIGHT (w);
+  min_y = WINDOW_TAB_LINE_HEIGHT (w) + WINDOW_HEADER_LINE_HEIGHT (w);
   from_y = WINDOW_TO_FRAME_PIXEL_Y (w, max (min_y, w->output_cursor.y));
   to_y = WINDOW_TO_FRAME_PIXEL_Y (w, to_y);
 
@@ -29972,6 +30822,7 @@ erase_phys_cursor (struct window *w)
   if (w->phys_cursor_type == HOLLOW_BOX_CURSOR)
     {
       int x, y;
+      int tab_line_height = WINDOW_TAB_LINE_HEIGHT (w);
       int header_line_height = WINDOW_HEADER_LINE_HEIGHT (w);
       int width;
 
@@ -29987,7 +30838,7 @@ erase_phys_cursor (struct window *w)
          x = 0;
        }
       width = min (width, window_box_width (w, TEXT_AREA) - x);
-      y = WINDOW_TO_FRAME_PIXEL_Y (w, max (header_line_height, cursor_row->y));
+      y = WINDOW_TO_FRAME_PIXEL_Y (w, max (tab_line_height, max 
(header_line_height, cursor_row->y)));
       x = WINDOW_TEXT_TO_FRAME_PIXEL_X (w, x);
 
       if (width > 0)
@@ -30333,12 +31184,13 @@ show_mouse_face (Mouse_HLInfo *hlinfo, enum 
draw_glyphs_face draw)
   /* Change the mouse cursor.  */
   if (FRAME_WINDOW_P (f) && NILP (track_mouse))
     {
-#ifndef HAVE_EXT_TOOL_BAR
       if (draw == DRAW_NORMAL_TEXT
-         && !EQ (hlinfo->mouse_face_window, f->tool_bar_window))
+#ifndef HAVE_EXT_TOOL_BAR
+         && !EQ (hlinfo->mouse_face_window, f->tool_bar_window)
+#endif
+         && !EQ (hlinfo->mouse_face_window, f->tab_bar_window))
        FRAME_RIF (f)->define_frame_cursor (f, FRAME_OUTPUT_DATA 
(f)->text_cursor);
       else
-#endif
       if (draw == DRAW_MOUSE_FACE)
        FRAME_RIF (f)->define_frame_cursor (f, FRAME_OUTPUT_DATA 
(f)->hand_cursor);
       else
@@ -31334,7 +32186,7 @@ note_mode_line_or_margin_highlight (Lisp_Object window, 
int x, int y,
   struct glyph * glyph = NULL, * row_start_glyph = NULL;
   struct glyph_row *row UNINIT;
 
-  if (area == ON_MODE_LINE || area == ON_HEADER_LINE)
+  if (area == ON_MODE_LINE || area == ON_HEADER_LINE || area == ON_TAB_LINE)
     {
       int x0;
       struct glyph *end;
@@ -31346,7 +32198,9 @@ note_mode_line_or_margin_highlight (Lisp_Object window, 
int x, int y,
 
       row = (area == ON_MODE_LINE
             ? MATRIX_MODE_LINE_ROW (w->current_matrix)
-            : MATRIX_HEADER_LINE_ROW (w->current_matrix));
+            : (area == ON_TAB_LINE
+                ? MATRIX_TAB_LINE_ROW (w->current_matrix)
+                : MATRIX_HEADER_LINE_ROW (w->current_matrix)));
 
       /* Find the glyph under the mouse pointer.  */
       if (row->mode_line_p && row->enabled_p)
@@ -31461,7 +32315,7 @@ note_mode_line_or_margin_highlight (Lisp_Object window, 
int x, int y,
 
              /* Change the mouse pointer according to what is under X/Y.  */
              if (NILP (pointer)
-                 && (area == ON_MODE_LINE || area == ON_HEADER_LINE))
+                 && (area == ON_MODE_LINE || area == ON_HEADER_LINE || area == 
ON_TAB_LINE))
                {
                  Lisp_Object map;
 
@@ -31487,7 +32341,7 @@ note_mode_line_or_margin_highlight (Lisp_Object window, 
int x, int y,
     {
       mouse_face = Fget_text_property (pos, Qmouse_face, string);
       if (!NILP (Vmouse_highlight) && !NILP (mouse_face)
-         && ((area == ON_MODE_LINE) || (area == ON_HEADER_LINE))
+         && ((area == ON_MODE_LINE) || (area == ON_HEADER_LINE) || (area == 
ON_TAB_LINE))
          && glyph)
        {
          Lisp_Object b, e;
@@ -31558,7 +32412,11 @@ note_mode_line_or_margin_highlight (Lisp_Object 
window, int x, int y,
          hpos = x - gpos;
          vpos = (area == ON_MODE_LINE
                  ? (w->current_matrix)->nrows - 1
-                 : 0);
+                 : (area == ON_TAB_LINE
+                     ? 0
+                     : (w->current_matrix->tab_line_p
+                        ? 1
+                        : 0)));
 
          /* If GLYPH's position is included in the region that is
             already drawn in mouse face, we have nothing to do.  */
@@ -31614,7 +32472,7 @@ note_mode_line_or_margin_highlight (Lisp_Object window, 
int x, int y,
 
   /* If mouse-face doesn't need to be shown, clear any existing
      mouse-face.  */
-  if ((area == ON_MODE_LINE || area == ON_HEADER_LINE) && !mouse_face_shown)
+  if ((area == ON_MODE_LINE || area == ON_HEADER_LINE || area == ON_TAB_LINE) 
&& !mouse_face_shown)
     clear_mouse_face (hlinfo);
 
   define_frame_cursor1 (f, cursor, pointer);
@@ -31658,7 +32516,7 @@ note_mouse_highlight (struct frame *f, int x, int y)
     return;
 
   /* Which window is that in?  */
-  window = window_from_coordinates (f, x, y, &part, true);
+  window = window_from_coordinates (f, x, y, &part, true, true);
 
   /* If displaying active text in another window, clear that.  */
   if (! EQ (window, hlinfo->mouse_face_window)
@@ -31667,7 +32525,8 @@ note_mouse_highlight (struct frame *f, int x, int y)
          && !NILP (window)
          && part != ON_TEXT
          && part != ON_MODE_LINE
-         && part != ON_HEADER_LINE))
+         && part != ON_HEADER_LINE
+         && part != ON_TAB_LINE))
     clear_mouse_face (hlinfo);
 
   /* Reset help_echo_string. It will get recomputed below.  */
@@ -31735,6 +32594,16 @@ note_mouse_highlight (struct frame *f, int x, int y)
   w = XWINDOW (window);
   frame_to_window_pixel_xy (w, &x, &y);
 
+#if defined (HAVE_WINDOW_SYSTEM)
+  /* Handle tab-bar window differently since it doesn't display a
+     buffer.  */
+  if (EQ (window, f->tab_bar_window))
+    {
+      note_tab_bar_highlight (f, x, y);
+      return;
+    }
+#endif
+
 #if defined (HAVE_WINDOW_SYSTEM) && ! defined (HAVE_EXT_TOOL_BAR)
   /* Handle tool-bar window differently since it doesn't display a
      buffer.  */
@@ -31746,7 +32615,7 @@ note_mouse_highlight (struct frame *f, int x, int y)
 #endif
 
   /* Mouse is on the mode, header line or margin?  */
-  if (part == ON_MODE_LINE || part == ON_HEADER_LINE
+  if (part == ON_MODE_LINE || part == ON_HEADER_LINE || part == ON_TAB_LINE
       || part == ON_LEFT_MARGIN || part == ON_RIGHT_MARGIN)
     {
       note_mode_line_or_margin_highlight (window, x, y, part);
@@ -32761,6 +33630,10 @@ expose_frame (struct frame *f, int x, int y, int w, 
int h)
                   r.x, r.y, r.width, r.height);
   mouse_face_overwritten_p = expose_window_tree (XWINDOW (f->root_window), &r);
 
+  if (WINDOWP (f->tab_bar_window))
+    mouse_face_overwritten_p
+      |= expose_window (XWINDOW (f->tab_bar_window), &r);
+
 #ifndef HAVE_EXT_TOOL_BAR
   if (WINDOWP (f->tool_bar_window))
     mouse_face_overwritten_p
@@ -32901,11 +33774,13 @@ be let-bound around code that needs to disable 
messages temporarily. */);
   defsubr (&Sdump_frame_glyph_matrix);
   defsubr (&Sdump_glyph_matrix);
   defsubr (&Sdump_glyph_row);
+  defsubr (&Sdump_tab_bar_row);
   defsubr (&Sdump_tool_bar_row);
   defsubr (&Strace_redisplay);
   defsubr (&Strace_to_stderr);
 #endif
 #ifdef HAVE_WINDOW_SYSTEM
+  defsubr (&Stab_bar_height);
   defsubr (&Stool_bar_height);
   defsubr (&Slookup_image_map);
 #endif
@@ -33291,6 +34166,18 @@ make sure that (1) your window manager has focus 
follow the mouse and
 of your window manager.  */);
   Vmouse_autoselect_window = Qnil;
 
+  DEFVAR_LISP ("auto-resize-tab-bars", Vauto_resize_tab_bars,
+    doc: /* Non-nil means automatically resize tab-bars.
+This dynamically changes the tab-bar's height to the minimum height
+that is needed to make all tab-bar items visible.
+If value is `grow-only', the tab-bar's height is only increased
+automatically; to decrease the tab-bar height, use \\[recenter].  */);
+  Vauto_resize_tab_bars = Qt;
+
+  DEFVAR_BOOL ("auto-raise-tab-bar-buttons", auto_raise_tab_bar_buttons_p,
+    doc: /* Non-nil means raise tab-bar buttons when the mouse moves over 
them.  */);
+  auto_raise_tab_bar_buttons_p = true;
+
   DEFVAR_LISP ("auto-resize-tool-bars", Vauto_resize_tool_bars,
     doc: /* Non-nil means automatically resize tool-bars.
 This dynamically changes the tool-bar's height to the minimum height
@@ -33313,6 +34200,30 @@ window, nil if it's okay to leave the cursor 
partially-visible.  */);
   Vmake_cursor_line_fully_visible = Qt;
   DEFSYM (Qmake_cursor_line_fully_visible, "make-cursor-line-fully-visible");
 
+  DEFVAR_LISP ("tab-bar-border", Vtab_bar_border,
+    doc: /* Border below tab-bar in pixels.
+If an integer, use it as the height of the border.
+If it is one of `internal-border-width' or `border-width', use the
+value of the corresponding frame parameter.
+Otherwise, no border is added below the tab-bar.  */);
+  Vtab_bar_border = Qinternal_border_width;
+
+  DEFVAR_LISP ("tab-bar-button-margin", Vtab_bar_button_margin,
+    doc: /* Margin around tab-bar buttons in pixels.
+If an integer, use that for both horizontal and vertical margins.
+Otherwise, value should be a pair of integers `(HORZ . VERT)' with
+HORZ specifying the horizontal margin, and VERT specifying the
+vertical margin.  */);
+  Vtab_bar_button_margin = make_fixnum (DEFAULT_TAB_BAR_BUTTON_MARGIN);
+
+  DEFVAR_INT ("tab-bar-button-relief", tab_bar_button_relief,
+    doc: /* Relief thickness of tab-bar buttons.  */);
+  tab_bar_button_relief = DEFAULT_TAB_BAR_BUTTON_RELIEF;
+
+  DEFVAR_INT ("tab-bar-max-label-size", tab_bar_max_label_size,
+    doc: /* Maximum number of characters a label can have to be shown.  */);
+  tab_bar_max_label_size = DEFAULT_TAB_BAR_LABEL_SIZE;
+
   DEFVAR_LISP ("tool-bar-border", Vtool_bar_border,
     doc: /* Border below tool-bar in pixels.
 If an integer, use it as the height of the border.
diff --git a/src/xfaces.c b/src/xfaces.c
index c3cae7e..ccf3379 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -4586,6 +4586,8 @@ lookup_basic_face (struct window *w, struct frame *f, int 
face_id)
     case MODE_LINE_FACE_ID:            name = Qmode_line;              break;
     case MODE_LINE_INACTIVE_FACE_ID:   name = Qmode_line_inactive;     break;
     case HEADER_LINE_FACE_ID:          name = Qheader_line;            break;
+    case TAB_LINE_FACE_ID:             name = Qtab_line;               break;
+    case TAB_BAR_FACE_ID:              name = Qtab_bar;                break;
     case TOOL_BAR_FACE_ID:             name = Qtool_bar;               break;
     case FRINGE_FACE_ID:               name = Qfringe;                 break;
     case SCROLL_BAR_FACE_ID:           name = Qscroll_bar;             break;
@@ -5293,6 +5295,8 @@ realize_basic_faces (struct frame *f)
       realize_named_face (f, Qwindow_divider_last_pixel,
                          WINDOW_DIVIDER_LAST_PIXEL_FACE_ID);
       realize_named_face (f, Qinternal_border, INTERNAL_BORDER_FACE_ID);
+      realize_named_face (f, Qtab_bar, TAB_BAR_FACE_ID);
+      realize_named_face (f, Qtab_line, TAB_LINE_FACE_ID);
 
       /* Reflect changes in the `menu' face in menu bars.  */
       if (FRAME_FACE_CACHE (f)->menu_face_changed_p)
@@ -6579,8 +6583,10 @@ syms_of_xfaces (void)
   /* Names of basic faces.  */
   DEFSYM (Qdefault, "default");
   DEFSYM (Qtool_bar, "tool-bar");
+  DEFSYM (Qtab_bar, "tab-bar");
   DEFSYM (Qfringe, "fringe");
   DEFSYM (Qheader_line, "header-line");
+  DEFSYM (Qtab_line, "tab-line");
   DEFSYM (Qscroll_bar, "scroll-bar");
   DEFSYM (Qmenu, "menu");
   DEFSYM (Qcursor, "cursor");
diff --git a/src/xfns.c b/src/xfns.c
index 31ae4cc..be869fd 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -1602,6 +1602,94 @@ x_set_menu_bar_lines (struct frame *f, Lisp_Object 
value, Lisp_Object oldval)
 }
 
 
+/* Set the number of lines used for the tab bar of frame F to VALUE.
+   VALUE not an integer, or < 0 means set the lines to zero.  OLDVAL
+   is the old number of tab bar lines.  This function changes the
+   height of all windows on frame F to match the new tab bar height.
+   The frame's height doesn't change.  */
+
+static void
+x_set_tab_bar_lines (struct frame *f, Lisp_Object value, Lisp_Object oldval)
+{
+  int nlines;
+
+  /* Treat tab bars like menu bars.  */
+  if (FRAME_MINIBUF_ONLY_P (f))
+    return;
+
+  /* Use VALUE only if an int >= 0.  */
+  if (RANGED_FIXNUMP (0, value, INT_MAX))
+    nlines = XFIXNAT (value);
+  else
+    nlines = 0;
+
+  x_change_tab_bar_height (f, nlines * FRAME_LINE_HEIGHT (f));
+}
+
+
+/* Set the pixel height of the tab bar of frame F to HEIGHT.  */
+void
+x_change_tab_bar_height (struct frame *f, int height)
+{
+  int unit = FRAME_LINE_HEIGHT (f);
+  int old_height = FRAME_TAB_BAR_HEIGHT (f);
+  int lines = (height + unit - 1) / unit;
+  Lisp_Object fullscreen;
+
+  /* Make sure we redisplay all windows in this frame.  */
+  fset_redisplay (f);
+
+  /* Recalculate tab bar and frame text sizes.  */
+  FRAME_TAB_BAR_HEIGHT (f) = height;
+  FRAME_TAB_BAR_LINES (f) = lines;
+  /* Store the `tab-bar-lines' and `height' frame parameters.  */
+  store_frame_param (f, Qtab_bar_lines, make_fixnum (lines));
+  store_frame_param (f, Qheight, make_fixnum (FRAME_LINES (f)));
+
+  /* We also have to make sure that the internal border at the top of
+     the frame, below the menu bar or tab bar, is redrawn when the
+     tab bar disappears.  This is so because the internal border is
+     below the tab bar if one is displayed, but is below the menu bar
+     if there isn't a tab bar.  The tab bar draws into the area
+     below the menu bar.  */
+  if (FRAME_X_WINDOW (f) && FRAME_TAB_BAR_HEIGHT (f) == 0)
+    {
+      clear_frame (f);
+      clear_current_matrices (f);
+    }
+
+  if ((height < old_height) && WINDOWP (f->tab_bar_window))
+    clear_glyph_matrix (XWINDOW (f->tab_bar_window)->current_matrix);
+
+  /* Recalculate tabbar height.  */
+  f->n_tab_bar_rows = 0;
+  if (old_height == 0
+      && (!f->after_make_frame
+         || NILP (frame_inhibit_implied_resize)
+         || (CONSP (frame_inhibit_implied_resize)
+             && NILP (Fmemq (Qtab_bar_lines, frame_inhibit_implied_resize)))))
+    f->tab_bar_redisplayed = f->tab_bar_resized = false;
+
+  adjust_frame_size (f, -1, -1,
+                    ((!f->tab_bar_resized
+                      && (NILP (fullscreen =
+                                get_frame_param (f, Qfullscreen))
+                          || EQ (fullscreen, Qfullwidth))) ? 1
+                     : (old_height == 0 || height == 0) ? 2
+                     : 4),
+                    false, Qtab_bar_lines);
+
+  f->tab_bar_resized = f->tab_bar_redisplayed;
+
+  /* adjust_frame_size might not have done anything, garbage frame
+     here.  */
+  adjust_frame_glyphs (f);
+  SET_FRAME_GARBAGED (f);
+  if (FRAME_X_WINDOW (f))
+    x_clear_under_internal_border (f);
+}
+
+
 /* Set the number of lines used for the tool bar of frame F to VALUE.
    VALUE not an integer, or < 0 means set the lines to zero.  OLDVAL
    is the old number of tool bar lines.  This function changes the
@@ -2732,6 +2820,7 @@ xic_set_statusarea (struct frame *f)
   area.x = FRAME_PIXEL_WIDTH (f) - area.width - FRAME_INTERNAL_BORDER_WIDTH 
(f);
   area.y = (FRAME_PIXEL_HEIGHT (f) - area.height
            - FRAME_MENUBAR_HEIGHT (f)
+           - FRAME_TABBAR_TOP_HEIGHT (f)
            - FRAME_TOOLBAR_TOP_HEIGHT (f)
             - FRAME_INTERNAL_BORDER_WIDTH (f));
   XFree (needed);
@@ -3922,6 +4011,10 @@ This function is an internal primitive--use `make-frame' 
instead.  */)
                          NILP (Vmenu_bar_mode)
                          ? make_fixnum (0) : make_fixnum (1),
                          NULL, NULL, RES_TYPE_NUMBER);
+  gui_default_parameter (f, parms, Qtab_bar_lines,
+                         NILP (Vtab_bar_mode)
+                         ? make_fixnum (0) : make_fixnum (1),
+                         NULL, NULL, RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qtool_bar_lines,
                          NILP (Vtool_bar_mode)
                          ? make_fixnum (0) : make_fixnum (1),
@@ -3941,7 +4034,7 @@ This function is an internal primitive--use `make-frame' 
instead.  */)
                          RES_TYPE_BOOLEAN);
 
   /* Compute the size of the X window.  */
-  window_prompting = gui_figure_window_size (f, parms, true,
+  window_prompting = gui_figure_window_size (f, parms, true, true,
                                              &x_width, &x_height);
 
   tem = gui_display_get_arg (dpyinfo, parms, Qunsplittable, 0, 0,
@@ -5060,6 +5153,7 @@ frame_geometry (Lisp_Object frame, Lisp_Object attribute)
   int internal_border_width;
   bool menu_bar_external = false, tool_bar_external = false;
   int menu_bar_height = 0, menu_bar_width = 0;
+  int tab_bar_height = 0, tab_bar_width = 0;
   int tool_bar_height = 0, tool_bar_width = 0;
 
   if (FRAME_INITIAL_P (f) || !FRAME_X_P (f) || !FRAME_OUTER_WINDOW (f))
@@ -5130,6 +5224,12 @@ frame_geometry (Lisp_Object frame, Lisp_Object attribute)
 #endif
   menu_bar_width = menu_bar_height ? native_width : 0;
 
+  tab_bar_height = FRAME_TAB_BAR_HEIGHT (f);
+  tab_bar_width = (tab_bar_height
+                   ? native_width - 2 * internal_border_width
+                   : 0);
+  inner_top += tab_bar_height;
+
 #ifdef HAVE_EXT_TOOL_BAR
   tool_bar_external = true;
   if (EQ (FRAME_TOOL_BAR_POSITION (f), Qleft))
@@ -5198,6 +5298,9 @@ frame_geometry (Lisp_Object frame, Lisp_Object attribute)
             Fcons (Qmenu_bar_size,
                    Fcons (make_fixnum (menu_bar_width),
                           make_fixnum (menu_bar_height))),
+            Fcons (Qtab_bar_size,
+                   Fcons (make_fixnum (tab_bar_width),
+                          make_fixnum (tab_bar_height))),
             Fcons (Qtool_bar_external, tool_bar_external ? Qt : Qnil),
             Fcons (Qtool_bar_position, FRAME_TOOL_BAR_POSITION (f)),
             Fcons (Qtool_bar_size,
@@ -6331,7 +6434,7 @@ x_create_tip_frame (struct x_display_info *dpyinfo, 
Lisp_Object parms)
                          "inhibitDoubleBuffering", "InhibitDoubleBuffering",
                          RES_TYPE_BOOLEAN);
 
-  gui_figure_window_size (f, parms, false, &x_width, &x_height);
+  gui_figure_window_size (f, parms, false, false, &x_width, &x_height);
 
   {
     XSetWindowAttributes attrs;
@@ -7672,6 +7775,7 @@ frame_parm_handler x_frame_parm_handlers[] =
   gui_set_vertical_scroll_bars,
   gui_set_horizontal_scroll_bars,
   gui_set_visibility,
+  x_set_tab_bar_lines,
   x_set_tool_bar_lines,
   x_set_scroll_bar_foreground,
   x_set_scroll_bar_background,
diff --git a/src/xterm.c b/src/xterm.c
index b761eaf..9e5ff79 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -3220,9 +3220,11 @@ x_draw_image_relief (struct glyph_string *s)
   if (s->hl == DRAW_IMAGE_SUNKEN
       || s->hl == DRAW_IMAGE_RAISED)
     {
-      thick = (tool_bar_button_relief < 0
-              ? DEFAULT_TOOL_BAR_BUTTON_RELIEF
-              : min (tool_bar_button_relief, 1000000));
+      thick = (tab_bar_button_relief < 0
+              ? DEFAULT_TAB_BAR_BUTTON_RELIEF
+              : (tool_bar_button_relief < 0
+                  ? DEFAULT_TOOL_BAR_BUTTON_RELIEF
+                  : min (tool_bar_button_relief, 1000000)));
       raised_p = s->hl == DRAW_IMAGE_RAISED;
     }
   else
@@ -3235,6 +3237,19 @@ x_draw_image_relief (struct glyph_string *s)
   y1 = y + s->slice.height - 1;
 
   extra_x = extra_y = 0;
+  if (s->face->id == TAB_BAR_FACE_ID)
+    {
+      if (CONSP (Vtab_bar_button_margin)
+         && FIXNUMP (XCAR (Vtab_bar_button_margin))
+         && FIXNUMP (XCDR (Vtab_bar_button_margin)))
+       {
+         extra_x = XFIXNUM (XCAR (Vtab_bar_button_margin));
+         extra_y = XFIXNUM (XCDR (Vtab_bar_button_margin));
+       }
+      else if (FIXNUMP (Vtab_bar_button_margin))
+       extra_x = extra_y = XFIXNUM (Vtab_bar_button_margin);
+    }
+
   if (s->face->id == TOOL_BAR_FACE_ID)
     {
       if (CONSP (Vtool_bar_button_margin)
@@ -8394,10 +8409,11 @@ handle_one_xevent (struct x_display_info *dpyinfo,
       /* If mouse-highlight is an integer, input clears out
         mouse highlighting.  */
       if (!hlinfo->mouse_face_hidden && FIXNUMP (Vmouse_highlight)
-#if ! defined (USE_GTK)
          && (f == 0
-             || !EQ (f->tool_bar_window, hlinfo->mouse_face_window))
+#if ! defined (USE_GTK)
+             || !EQ (f->tool_bar_window, hlinfo->mouse_face_window)
 #endif
+             || !EQ (f->tab_bar_window, hlinfo->mouse_face_window))
          )
         {
           clear_mouse_face (hlinfo);
@@ -8821,7 +8837,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
              {
                static Lisp_Object last_mouse_window;
                Lisp_Object window = window_from_coordinates
-                 (f, event->xmotion.x, event->xmotion.y, 0, false);
+                 (f, event->xmotion.x, event->xmotion.y, 0, false, false);
 
                /* A window will be autoselected only when it is not
                   selected now and the last mouse movement event was
@@ -9032,6 +9048,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
       {
         /* If we decide we want to generate an event to be seen
            by the rest of Emacs, we put it here.  */
+        bool tab_bar_p = false;
         bool tool_bar_p = false;
 
        memset (&compose_status, 0, sizeof (compose_status));
@@ -9068,6 +9085,23 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 #endif
         if (f)
           {
+            /* Is this in the tab-bar?  */
+            if (WINDOWP (f->tab_bar_window)
+                && WINDOW_TOTAL_LINES (XWINDOW (f->tab_bar_window)))
+              {
+                Lisp_Object window;
+                int x = event->xbutton.x;
+                int y = event->xbutton.y;
+
+                window = window_from_coordinates (f, x, y, 0, true, true);
+                tab_bar_p = EQ (window, f->tab_bar_window);
+
+                if (tab_bar_p && event->xbutton.button < 4)
+                 handle_tab_bar_click
+                   (f, x, y, event->xbutton.type == ButtonPress,
+                    x_x_to_emacs_modifiers (dpyinfo, event->xbutton.state));
+              }
+
 #if ! defined (USE_GTK)
             /* Is this in the tool-bar?  */
             if (WINDOWP (f->tool_bar_window)
@@ -9077,7 +9111,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                 int x = event->xbutton.x;
                 int y = event->xbutton.y;
 
-                window = window_from_coordinates (f, x, y, 0, true);
+                window = window_from_coordinates (f, x, y, 0, true, true);
                 tool_bar_p = EQ (window, f->tool_bar_window);
 
                 if (tool_bar_p && event->xbutton.button < 4)
@@ -9087,7 +9121,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
               }
 #endif /* !USE_GTK */
 
-            if (!tool_bar_p)
+            if (!tab_bar_p && !tool_bar_p)
 #if defined (USE_X_TOOLKIT) || defined (USE_GTK)
               if (! popup_activated ())
 #endif
@@ -9134,6 +9168,8 @@ handle_one_xevent (struct x_display_info *dpyinfo,
           {
             dpyinfo->grabbed |= (1 << event->xbutton.button);
             dpyinfo->last_mouse_frame = f;
+            if (f && !tab_bar_p)
+              f->last_tab_bar_item = -1;
 #if ! defined (USE_GTK)
             if (f && !tool_bar_p)
               f->last_tool_bar_item = -1;
@@ -11346,8 +11382,10 @@ x_set_window_size_1 (struct frame *f, bool 
change_gravity,
     {
       frame_size_history_add
        (f, Qx_set_window_size_3, width, height,
-        list3i (pixelwidth + FRAME_TOOLBAR_WIDTH (f),
+        list3i (pixelwidth + FRAME_TOOLBAR_WIDTH (f)
+                 + FRAME_TABBAR_WIDTH (f),
                 (pixelheight + FRAME_TOOLBAR_HEIGHT (f)
+                  + FRAME_TABBAR_HEIGHT (f)
                  + FRAME_MENUBAR_HEIGHT (f)),
                 FRAME_MENUBAR_HEIGHT (f)));
 
@@ -13464,6 +13502,7 @@ x_create_terminal (struct x_display_info *dpyinfo)
 #if defined (USE_X_TOOLKIT) || defined (USE_GTK)
   terminal->popup_dialog_hook = xw_popup_dialog;
 #endif
+  terminal->change_tab_bar_height_hook = x_change_tab_bar_height;
 #ifndef HAVE_EXT_TOOL_BAR
   terminal->change_tool_bar_height_hook = x_change_tool_bar_height;
 #endif
diff --git a/src/xterm.h b/src/xterm.h
index 985648a..5b4d47d 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -505,6 +505,16 @@ struct x_output
   int menubar_height;
 #endif
 
+  /* Height of tab bar widget, in pixels.  top_height is used if tab bar
+     at top, bottom_height if tab bar is at the bottom.
+     Zero if not using an external tab bar or if tab bar is vertical.  */
+  int tabbar_top_height, tabbar_bottom_height;
+
+  /* Width of tab bar widget, in pixels.  left_width is used if tab bar
+     at left, right_width if tab bar is at the right.
+     Zero if not using an external tab bar or if tab bar is horizontal.  */
+  int tabbar_left_width, tabbar_right_width;
+
   /* Height of tool bar widget, in pixels.  top_height is used if tool bar
      at top, bottom_height if tool bar is at the bottom.
      Zero if not using an external tool bar or if tool bar is vertical.  */
@@ -572,6 +582,11 @@ struct x_output
   GtkWidget *hbox_widget;
   /* The menubar in this frame.  */
   GtkWidget *menubar_widget;
+  /* The tab bar in this frame  */
+  GtkWidget *tabbar_widget;
+  /* True if tab bar is packed into the hbox widget (i.e. vertical).  */
+  bool_bf tabbar_in_hbox : 1;
+  bool_bf tabbar_is_packed : 1;
   /* The tool bar in this frame  */
   GtkWidget *toolbar_widget;
   /* True if tool bar is packed into the hbox widget (i.e. vertical).  */
@@ -815,6 +830,15 @@ extern void x_mark_frame_dirty (struct frame *f);
 
 #define FRAME_FONT(f) ((f)->output_data.x->font)
 #define FRAME_FONTSET(f) ((f)->output_data.x->fontset)
+#define FRAME_TABBAR_TOP_HEIGHT(f) ((f)->output_data.x->tabbar_top_height)
+#define FRAME_TABBAR_BOTTOM_HEIGHT(f) \
+  ((f)->output_data.x->tabbar_bottom_height)
+#define FRAME_TABBAR_HEIGHT(f) \
+  (FRAME_TABBAR_TOP_HEIGHT (f) + FRAME_TABBAR_BOTTOM_HEIGHT (f))
+#define FRAME_TABBAR_LEFT_WIDTH(f) ((f)->output_data.x->tabbar_left_width)
+#define FRAME_TABBAR_RIGHT_WIDTH(f) ((f)->output_data.x->tabbar_right_width)
+#define FRAME_TABBAR_WIDTH(f) \
+  (FRAME_TABBAR_LEFT_WIDTH (f) + FRAME_TABBAR_RIGHT_WIDTH (f))
 #define FRAME_TOOLBAR_TOP_HEIGHT(f) ((f)->output_data.x->toolbar_top_height)
 #define FRAME_TOOLBAR_BOTTOM_HEIGHT(f) \
   ((f)->output_data.x->toolbar_bottom_height)
@@ -1178,6 +1202,7 @@ extern void initial_set_up_x_back_buffer (struct frame 
*f);
 
 /* Defined in xfns.c.  */
 extern void x_real_positions (struct frame *, int *, int *);
+extern void x_change_tab_bar_height (struct frame *, int);
 extern void x_change_tool_bar_height (struct frame *, int);
 extern void x_implicitly_set_name (struct frame *, Lisp_Object, Lisp_Object);
 extern void x_set_scroll_bar_default_width (struct frame *);



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