diff --git a/Makefile.in b/Makefile.in
--- a/Makefile.in
+++ b/Makefile.in
@@ -134,7 +134,7 @@
 	   style/acronym.el   style/xparse.el    style/fancyvrb.el \
 	   style/tabulary.el  style/fontspec.el  style/unicode-math.el \
 	   style/luacode.el   style/metalogo.el  style/english.el \
-	   style/exercise.el
+	   style/exercise.el  style/plext.el
 STYLEELC = $(STYLESRC:.el=.elc)
 
 CLEANFILES = $(AUCELC) $(STYLEELC) $(MULEELC)
diff --git a/latex.el b/latex.el
--- a/latex.el
+++ b/latex.el
@@ -1028,7 +1028,8 @@
 			      (concat
 			       (unless (zerop (length pos))
 				 (concat LaTeX-optop pos LaTeX-optcl))
-			       (concat TeX-grop fmt TeX-grcl)))))
+			       (concat TeX-grop fmt TeX-grcl)))
+    (LaTeX-item-array t)))
 
 (defun LaTeX-env-label (environment)
   "Insert ENVIRONMENT and prompt for label."
@@ -1076,7 +1077,8 @@
 			       (concat TeX-grop width TeX-grcl) ;; not optional!
 			       (unless (zerop (length pos))
 				 (concat LaTeX-optop pos LaTeX-optcl))
-			       (concat TeX-grop fmt TeX-grcl)))))
+			       (concat TeX-grop fmt TeX-grcl)))
+    (LaTeX-item-tabular* t)))
 
 (defun LaTeX-env-picture (environment)
   "Insert ENVIRONMENT with width, height specifications."
@@ -1154,6 +1156,126 @@
   "Insert a new bibitem."
   (TeX-insert-macro "bibitem"))
 
+(defun LaTeX-item-array (&optional suppress)
+  "Insert line break macro on the last line and suitable number of &'s.
+For array and tabular environments.
+
+If SUPPRESS is non-nil, do not insert line break macro."
+  (unless suppress
+    (save-excursion
+      (end-of-line 0)
+      (just-one-space)
+      (TeX-insert-macro "\\")))
+  (LaTeX-insert-ampersands
+   LaTeX-array-skipping-regexp 'LaTeX-array-count-columns))
+
+(defun LaTeX-item-tabular* (&optional suppress)
+  "Insert line break macro on the last line and suitable number of &'s.
+For tabular* environment.
+
+If SUPPRESS is non-nil, do not insert line break macro."
+  (unless suppress
+    (save-excursion
+      (end-of-line 0)
+      (just-one-space)
+      (TeX-insert-macro "\\")))
+  (LaTeX-insert-ampersands
+   LaTeX-tabular*-skipping-regexp 'LaTeX-array-count-columns))
+
+(defvar LaTeX-array-skipping-regexp (regexp-opt '("[t]" "[b]" ""))
+   "Regexp matching between \\begin{xxx} and column specification.
+For array and tabular environments.  See `LaTeX-insert-ampersands' for
+detail.")
+
+(defvar LaTeX-tabular*-skipping-regexp
+  ;; Assume width specification contains neither nested curly brace
+  ;; pair nor escaped "}".
+  (concat "{[^}]*}[ \t]*" (regexp-opt '("[t]" "[b]" "")))
+   "Regexp matching between \\begin{tabular*} and column specification.
+For tabular* environment only.  See `LaTeX-insert-ampersands' for detail.")
+
+(defun LaTeX-insert-ampersands (regexp func)
+  "Insert suitable number of ampersands for the current environment.
+The number is calculated from REGEXP and FUNC.
+
+Example 1:
+Consider the case that the current environment begins with
+\\begin{array}[t]{|lcr|}
+.  REGEXP must be chosen to match \"[t]\", i.e., the text between just
+after \"\\begin{array}\" and just before \"{|lcr|}\", which encloses
+the column specification.  FUNC must return the number of ampersands to
+be inserted, which is 2 since this example specifies three columns.
+FUNC is called with two arguments START and END, which spans the column
+specification (without enclosing braces.)  REGEXP is used to determine
+these START and END.
+
+Example 2:
+This time the environment begins with
address@hidden,}p{5ex}}
+.  REGEXP must match \"{1.0\\linewidth}[b]\" and FUNC must return 1 from
+the text \"address@hidden,}p{5ex}\" between START and END specified two columns.
+
+FUNC should return nil if it cannot determine the number of ampersands."
+  (let* ((cur (point))
+	 (num
+	  (save-excursion
+	    (ignore-errors
+	      (LaTeX-find-matching-begin)
+	      ;; Skip over "\begin{xxx}" and possible whitespaces.
+	      (forward-list 1)
+	      (skip-chars-forward " \t")
+	      ;; Skip over the text specified by REGEXP and whitespaces.
+	      (when (let ((case-fold-search nil))
+		      (re-search-forward regexp cur))
+		(skip-chars-forward " \t")
+		(when (eq (following-char) ?{)
+		  ;; We have reached the target "{yyy}" part.
+		  (forward-char 1)
+		  ;; The next line doesn't move point, so point
+		  ;; is left just after the opening brace.
+		  (let ((pos (TeX-find-closing-brace)))
+		    (if pos
+			;; Calculate number of ampersands to be inserted.
+			(funcall func (point) (1- pos))))))))))
+    (if (natnump num)
+	(save-excursion (insert (make-string num ?&))))))
+
+(defvar LaTeX-array-column-letters "clrp"
+  "Column letters for array-like environments.
+See `LaTeX-array-count-columns' for detail.")
+
+(defun LaTeX-array-count-columns (start end)
+  "Count number of ampersands to be inserted.
+The columns are specified by the letters found in the string
+`LaTeX-array-column-letters' and the number of those letters within the
+text between START and END is basically considered to be the number of
+columns.  The arguments surrounded between braces such as p{30pt} do not
+interfere the count of columns.
+
+Return one less number than the column, or nil on failing to count the
+right number."
+  (save-excursion
+    (let (p (cols 0))
+      (goto-char start)
+      (while (< (setq p (point)) end)
+
+	;; The below block accounts for one unit of move for
+	;; one column.
+	(setq cols (+ cols (skip-chars-forward
+			    LaTeX-array-column-letters end)))
+	(skip-chars-forward (concat
+			     "^" LaTeX-array-column-letters
+			     TeX-grop) end)
+	(if (eq (following-char) ?{) (forward-list 1))
+
+	;; Not sure whether this is really necessary or not, but
+	;; prepare for possible infinite loop anyway.
+	(when (eq p (point))
+	  (setq cols nil)
+	  (goto-char end)))
+      ;; The number of ampersands is one less than column.
+      (if cols (1- cols)))))
+
 ;;; Parser
 
 (defvar LaTeX-auto-style nil)
@@ -5678,7 +5800,10 @@
 
   (make-local-variable 'LaTeX-item-list)
   (setq LaTeX-item-list '(("description" . LaTeX-item-argument)
-			  ("thebibliography" . LaTeX-item-bib)))
+			  ("thebibliography" . LaTeX-item-bib)
+			  ("array" . LaTeX-item-array)
+			  ("tabular" . LaTeX-item-array)
+			  ("tabular*" . LaTeX-item-tabular*)))
 
   (setq TeX-complete-list
 	(append '(("\\\\cite\\[[^]\n\r\\%]*\\]{\\([^{}\n\r\\%,]*\\)"
diff --git a/style/amsmath.el b/style/amsmath.el
--- a/style/amsmath.el
+++ b/style/amsmath.el
@@ -43,8 +43,8 @@
      '("xalignat"   LaTeX-amsmath-env-alignat)
      '("xalignat*"  LaTeX-amsmath-env-alignat)
      '("xxalignat"  LaTeX-amsmath-env-alignat)
-     '("aligned"    LaTeX-amsmath-env-aligned)
-     '("gathered"   LaTeX-amsmath-env-aligned)
+     '("aligned"    ["Vertical position (t or b)"])
+     '("gathered"   ["Vertical position (t or b)"])
      '("alignedat"  LaTeX-amsmath-env-alignedat)
      "align*" "gather*" "flalign*" "multline*" "equation*"
      "split"
@@ -104,19 +104,19 @@
 	   (append '(("split"    . LaTeX-item-equation)
 		     ("multline" . LaTeX-item-equation)
 		     ("multline*" . LaTeX-item-equation)
-		     ("gather"   . LaTeX-item-equations)
+		     ("gather"   . LaTeX-item-equation)
 		     ("gather*"  . LaTeX-item-equation)
 		     ("gathered" . LaTeX-item-equation)
-		     ("align"    . LaTeX-item-equations)
+		     ("align"    . LaTeX-item-equation)
 		     ("align*"   . LaTeX-item-equation)
 		     ("aligned"  . LaTeX-item-equation)
-		     ("alignat"  . LaTeX-item-equations)
-		     ("alignat*" . LaTeX-item-equation)
-		     ("xalignat"  . LaTeX-item-equations)
-		     ("xalignat*" . LaTeX-item-equation)
-		     ("xxalignat" . LaTeX-item-equation)
-		     ("alignedat" . LaTeX-item-equation)
-		     ("flalign"  . LaTeX-item-equations)
+		     ("alignat"  . LaTeX-item-equation-alignat)
+		     ("alignat*" . LaTeX-item-equation-alignat)
+		     ("xalignat"  . LaTeX-item-equation-alignat)
+		     ("xalignat*" . LaTeX-item-equation-alignat)
+		     ("xxalignat" . LaTeX-item-equation-alignat)
+		     ("alignedat" . LaTeX-item-equation-alignat)
+		     ("flalign"  . LaTeX-item-equation)
 		     ("flalign*" . LaTeX-item-equation)
 		     ("matrix" .  LaTeX-item-equation)
 		     ("pmatrix" .  LaTeX-item-equation)
@@ -136,7 +136,7 @@
 	  (append '(("align"      . LaTeX-amsmath-label)
 		    ("alignat"    . LaTeX-amsmath-label)
 		    ("xalignat"   . LaTeX-amsmath-label)
-		    ("multline"    . LaTeX-amsmath-label)
+		    ("multline"   . LaTeX-amsmath-label)
 		    ("flalign"    . LaTeX-amsmath-label)
 		    ("gather"     . LaTeX-amsmath-label))
 		  LaTeX-label-alist))
@@ -160,38 +160,43 @@
 (defun LaTeX-amsmath-env-alignat (env)
   (let ((ncols (read-string "Number of columns: ")))
     (LaTeX-insert-environment env (concat TeX-grop ncols TeX-grcl))
-    (and (not (string= "xxalignat" env))
-	 (not (string= "*" (substring env -1)))
-	 (LaTeX-label env)
-	 (newline-and-indent))))
-
-(defun LaTeX-amsmath-env-aligned (env)
-  (let ((where (read-string "(optional) Vertical position (t or b): ")))
-    (if (string= where "")
-	(setq where "")
-      (setq where (concat "[" where "]")))
-    (LaTeX-insert-environment env where)))
+    (LaTeX-item-equation-alignat t)))
 
 (defun LaTeX-amsmath-env-alignedat (env)
-  (let ((where (read-string "(optional) Vertical position (t or b): "))
-     (ncols (read-string "Number of columns: ")))
-    (if (string= where "")
-     (setq where "")
-      (setq where (concat "[" where "]")))
-    (LaTeX-insert-environment env (concat where TeX-grop ncols TeX-grcl))))
+  (let ((where (read-string "(Optional) Vertical position (t or b): "))
+	(ncols (read-string "Number of columns: ")))
+    (unless (string= where "")
+      (setq where (concat LaTeX-optop where LaTeX-optcl)))
+    (LaTeX-insert-environment env (concat where TeX-grop ncols TeX-grcl))
+    (LaTeX-item-equation-alignat t)))
 
-(defun LaTeX-item-equation ()
-  (end-of-line 0)
-  (just-one-space)
-  (insert "\\\\")
-  (forward-line 1)
-  (indent-according-to-mode))
+(defun LaTeX-item-equation (&optional suppress)
+  (unless suppress
+    (end-of-line 0)
+    (just-one-space)
+    (TeX-insert-macro "\\")
+    (forward-line 1)
+    (indent-according-to-mode))
+  (let ((env (LaTeX-current-environment)))
+    (when (and (assoc env LaTeX-label-alist)
+	       (LaTeX-label env))
+      (LaTeX-newline)
+      (indent-according-to-mode))))
 
-(defun LaTeX-item-equations ()
-  (LaTeX-item-equation)
-  (let ((environment (LaTeX-current-environment 1)))
-    (and (LaTeX-label environment)
-	 (newline-and-indent))))
+(defun LaTeX-item-equation-alignat (&optional suppress)
+  (LaTeX-item-equation suppress)
+  (LaTeX-insert-ampersands
+   (concat "\\(?:"
+	   (regexp-quote LaTeX-optop) "[tb]" (regexp-quote LaTeX-optcl)
+	   "\\)?")
+   'LaTeX-amsmath-alignat-number-of-ampersands))
+
+(defun LaTeX-amsmath-alignat-number-of-ampersands (start end)
+  "Return the number of ampersands to insert.
+The number is 2N-1 where N is the number taken from the text between
+START and END."
+  (let ((num (string-to-number (buffer-substring-no-properties start end))))
+    (if (integerp num) (+ num num -1))))
 
 (defvar LaTeX-amsmath-package-options '("intlimits" "nointlimits"
 					"sumlimits" "nosumlimits"
diff --git a/style/array.el b/style/array.el
--- a/style/array.el
+++ b/style/array.el
@@ -40,7 +40,10 @@
 
    ;; `array.sty' adds a couple of new lengths.  They're added here, rather than
    ;; in the `TeX-add-symbols' block.
-   (LaTeX-add-lengths "extratabsurround" "extrarowheight")))
+   (LaTeX-add-lengths "extratabsurround" "extrarowheight")
+
+   ;; `array.sty' adds some new column specification letters.
+   (set (make-local-variable 'LaTeX-array-column-letters) "clrpmb")))
 
 (defvar LaTeX-array-package-options nil
   "Package options for array.")
diff --git a/style/plext.el b/style/plext.el
new file mode 100644
--- /dev/null
+++ b/style/plext.el
@@ -0,0 +1,49 @@
+;;; plext.el --- Style hook for the pLaTeX plext package.
+
+;;; Code:
+
+(TeX-add-style-hook
+ "plext"
+ (lambda ()
+   ;; plext.sty extends some environments to accept option, e.g. <t>,
+   ;; for vertical typesetting.
+   (LaTeX-add-environments
+    ;; TODO: Add support for minipage and picture
+    ;; environments extension.
+    '("array"    LaTeX-plext-env-array)
+    '("tabular"  LaTeX-plext-env-array)
+    '("tabular*" LaTeX-plext-env-array))
+
+   (set (make-local-variable 'LaTeX-array-skipping-regexp)
+	(concat "\\(?:<[tyz]>\\)?[ \t]*" (regexp-opt '("[t]" "[b]" ""))))
+   (set (make-local-variable 'LaTeX-tabular*-skipping-regexp)
+	(concat "\\(?:<[tyz]>\\)?[ \t]*{[^}]*}[ \t]*"
+		(regexp-opt '("[t]" "[b]" ""))))))
+
+(defun LaTeX-plext-env-array (env)
+  (let ((dir (read-string "(Optional) Direction (t or y or z): "))
+	(width (if (string= env "tabular*")
+		   (read-string "Width: " LaTeX-default-width)))
+	(pos (and LaTeX-default-position ; LaTeX-default-position can
+					; be nil, i.e. do not prompt
+		  (read-string "(Optional) Position: " LaTeX-default-position)))
+	(fmt (read-string "Format: " LaTeX-default-format)))
+    (unless (zerop (length dir))
+      (setq dir (concat "<" dir ">")))
+    (if (string= env "tabular*")
+	(setq LaTeX-default-width width))
+    (setq LaTeX-default-position pos)
+    (setq LaTeX-default-format fmt)
+    (LaTeX-insert-environment env
+			      (concat
+			       dir
+			       (if (string= env "tabular*")
+				   (concat TeX-grop width TeX-grcl))
+			       (unless (zerop (length pos))
+				 (concat LaTeX-optop pos LaTeX-optcl))
+			       (concat TeX-grop fmt TeX-grcl)))
+    (if (string= env "tabular*")
+	(LaTeX-item-tabular* t)
+      (LaTeX-item-array t))))
+
+;;; plext.el ends here.