style: update comments

[Akim Demaille]

commit 0820f16ca8a140f2ef8261a9ab42301a7358cec2
Author: Akim Demaille <akim.demaille@gmail.com>
Date:   Sun Jul 5 08:34:39 2020 +0200

    style: update comments
    
    * src/reader.c: action_obstack was removed in 2002...
    * src/parse-gram.y: Better names.
    * src/scan-code.h: More comments.

diff --git a/data/skeletons/yacc.c b/data/skeletons/yacc.c
index 43838d01..9ec153ac 100644
--- a/data/skeletons/yacc.c
+++ b/data/skeletons/yacc.c
@@ -48,6 +48,10 @@ m4_define([b4_pure_if],
 ## api.push-pull.  ##
 ## --------------- ##
 
+# b4_pull_if, b4_push_if
+# ----------------------
+# Whether the pull/push APIs are needed.  Both can be enabled.
+
 b4_percent_define_default([[api.push-pull]], [[pull]])
 b4_percent_define_check_values([[[[api.push-pull]],
                                  [[pull]], [[push]], [[both]]]])
diff --git a/src/parse-gram.y b/src/parse-gram.y
index 4581fc73..fc046f60 100644
--- a/src/parse-gram.y
+++ b/src/parse-gram.y
@@ -695,8 +695,8 @@ rhs:
                                   current_lhs_named_ref); }
 | rhs symbol named_ref.opt
     { grammar_current_rule_symbol_append ($2, @2, $3); }
-| rhs tag.opt "{...}"[act] named_ref.opt[name]
-    { grammar_current_rule_action_append ($act, @act, $name, $[tag.opt]); }
+| rhs tag.opt "{...}"[action] named_ref.opt[name]
+    { grammar_current_rule_action_append ($action, @action, $name, 
$[tag.opt]); }
 | rhs "%?{...}"
     { grammar_current_rule_predicate_append ($2, @2); }
 | rhs "%empty"
diff --git a/src/reader.c b/src/reader.c
index 1ba710c6..2d142331 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -695,12 +695,10 @@ packgram (void)
 }
 
 
-/*------------------------------------------------------------------.
-| Read in the grammar specification and record it in the format     |
-| described in gram.h.  All actions are copied into ACTION_OBSTACK, |
-| in each case forming the body of a C function (YYACTION) which    |
-| contains a switch statement to decide which action to execute.    |
-`------------------------------------------------------------------*/
+/*--------------------------------------------------------------.
+| Read in the grammar specification and record it in the format |
+| described in gram.h.                                          |
+`--------------------------------------------------------------*/
 
 void
 reader (const char *gram)
diff --git a/src/scan-code.h b/src/scan-code.h
index 06b6a73a..3859e2b2 100644
--- a/src/scan-code.h
+++ b/src/scan-code.h
@@ -145,6 +145,7 @@ void code_props_symbol_action_init (code_props *self, char 
const *code,
                                     location code_loc);
 
 /**
+ * \param  type   type for midrule actions
  * \pre
  *   - <tt>self != NULL</tt>.
  *   - <tt>code != NULL</tt>.