Tweak C-x TAB behavior changes, and update docs.

* lisp/indent.el (indent-rigidly-map): Add docstring, and move commands
into named functions.
(indent-rigidly-left, indent-rigidly-right)
(indent-rigidly-left-to-tab-stop)
(indent-rigidly-right-to-tab-stop): New functions.  Decide on
indentation direction based on bidi direction, and accumulate
sequential commands in a single undo boundary.
(indent-rigidly--pop-undo): New utility function.

* doc/emacs/indent.texi (Indentation Commands): Document C-x TAB changes.

* doc/lispref/text.texi (Region Indent): Note the new interactive
behavior of indent-rigidly.

doc/emacs/ChangeLog

@@ -1,3 +1,7 @@
+2013-12-21  Chong Yidong  <cyd@gnu.org>
+
+	* indent.texi (Indentation Commands): Document C-x TAB changes.
+
 2013-12-20  Tassilo Horn  <tsdh@gnu.org>
 
 	* rmail.texi: Document `S-SPC' as alternative to scrolling down

doc/emacs/indent.texi

@@ -127,14 +127,26 @@ that column number.
 @kindex C-x TAB
 @findex indent-rigidly
 @cindex remove indentation
-Shift each line in the region by a fixed distance, to the right or
-left (@code{indent-rigidly}).  The distance to move is determined by
-the numeric argument (positive to move rightward, negative to move
-leftward).
+This command is used to change the indentation of all lines that begin
+in the region, moving the affected lines as a ``rigid'' unit.
 
-This command can be used to remove all indentation from the lines in
-the region, by invoking it with a large negative argument,
-e.g., @kbd{C-u -1000 C-x @key{TAB}}.
+If called with no argument, the command activates a transient mode for
+adjusting the indentation of the affected lines interactively.  While
+this transient mode is active, typing @key{LEFT} or @key{RIGHT}
+indents leftward and rightward, respectively, by one space.  You can
+also type @kbd{S-@key{LEFT}} or @kbd{S-@key{RIGHT}} to indent leftward
+or rightward to the next tab stop (@pxref{Tab Stops}).  Typing any
+other key disables the transient mode, and resumes normal editing.
+
+If called with a prefix argument @var{n}, this command indents the
+lines forward by @var{n} spaces (without enabling the transient mode).
+Negative values of @var{n} indent backward, so you can remove all
+indentation from the lines in the region using a large negative
+argument, like this:
+
+@smallexample
+C-u -999 C-x @key{TAB}
+@end smallexample
 @end table
 
 @node Tab Stops

doc/lispref/ChangeLog

@@ -1,3 +1,8 @@
+2013-12-21  Chong Yidong  <cyd@gnu.org>
+
+	* text.texi (Region Indent): Note the new interactive behavior of
+	indent-rigidly.
+
 2013-12-20  Tassilo Horn  <tsdh@gnu.org>
 
 	* numbers.texi (numbers): Document that =, <, <=, >, >= now accept

doc/lispref/text.texi

@@ -2344,21 +2344,19 @@ a different meaning and does not use this variable.
 @end defvar
 
 @deffn Command indent-rigidly start end count
-This command indents all lines starting between @var{start}
+This function indents all lines starting between @var{start}
 (inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
 This ``preserves the shape'' of the affected region, moving it as a
-rigid unit.  Consequently, this command is useful not only for indenting
-regions of unindented text, but also for indenting regions of formatted
-code.
+rigid unit.
 
-For example, if @var{count} is 3, this command adds 3 columns of
-indentation to each of the lines beginning in the region specified.
+This is useful not only for indenting regions of unindented text, but
+also for indenting regions of formatted code.  For example, if
+@var{count} is 3, this command adds 3 columns of indentation to every
+line that begins in the specified region.
 
-@c FIXME: I suggest using message-indent-citation as the example, or
-@c just remove this paragraph.  --xfq
-In Mail mode, @kbd{C-c C-y} (@code{mail-yank-original}) uses
-@code{indent-rigidly} to indent the text copied from the message being
-replied to.
+If called interactively with no prefix argument, this command invokes
+a transient mode for adjusting indentation rigidly.  @xref{Indentation
+Commands,,, emacs, The GNU Emacs Manual}.
 @end deffn
 
 @deffn Command indent-code-rigidly start end columns &optional nochange-regexp

lisp/ChangeLog

@@ -1,3 +1,14 @@
+2013-12-21  Chong Yidong  <cyd@gnu.org>
+
+	* indent.el (indent-rigidly-map): Add docstring, and move commands
+	into named functions.
+	(indent-rigidly-left, indent-rigidly-right)
+	(indent-rigidly-left-to-tab-stop)
+	(indent-rigidly-right-to-tab-stop): New functions.  Decide on
+	indentation direction based on bidi direction, and accumulate
+	sequential commands in a single undo boundary.
+	(indent-rigidly--pop-undo): New utility function.
+
 2013-12-20  Juanma Barranquero  <lekktu@gmail.com>
 
 	* faces.el (read-face-name): Require crm.el when using crm-separator.

lisp/indent.el

@@ -169,31 +169,28 @@ Blank lines are ignored."
 
 (defvar indent-rigidly-map
   (let ((map (make-sparse-keymap)))
-    (define-key map [left]
-      (lambda (beg end) (interactive "r") (indent-rigidly beg end -1)))
-
-    (define-key map [right]
-      (lambda (beg end) (interactive "r") (indent-rigidly beg end 1)))
-
-    (define-key map [S-right]
-      (lambda (beg end) (interactive "r")
-        (let* ((current (indent-rigidly--current-indentation beg end))
-               (next (indent--next-tab-stop current)))
-          (indent-rigidly beg end (- next current)))))
-
-    (define-key map [S-left]
-      (lambda (beg end) (interactive "r")
-        (let* ((current (indent-rigidly--current-indentation beg end))
-               (next (indent--next-tab-stop current 'prev)))
-          (indent-rigidly beg end (- next current)))))
-    map))
+    (define-key map [left]  'indent-rigidly-left)
+    (define-key map [right] 'indent-rigidly-right)
+    (define-key map [S-left]  'indent-rigidly-left-to-tab-stop)
+    (define-key map [S-right] 'indent-rigidly-right-to-tab-stop)
+    map)
+  "Transient keymap for adjusting indentation interactively.
+It is activated by calling `indent-rigidly' interactively.")
 
 (defun indent-rigidly (start end arg &optional interactive)
-  "Indent all lines starting in the region sideways by ARG columns.
-Called from a program, takes three arguments, START, END and ARG.
-You can remove all indentation from a region by giving a large negative ARG.
-If used interactively and no prefix argument is given, use a transient
-mode that lets you move the text with cursor keys."
+  "Indent all lines starting in the region.
+If called interactively with no prefix argument, activate a
+transient mode in which the indentation can be adjusted interactively
+by typing \\<indent-rigidly-map>\\[indent-rigidly-left], \\[indent-rigidly-right], \\[indent-rigidly-left-to-tab-stop], or \\[indent-rigidly-right-to-tab-stop].
+Typing any other key deactivates the transient mode.
+
+If called from a program, or interactively with prefix ARG,
+indent all lines starting in the region forward by ARG columns.
+If called from a program, START and END specify the beginning and
+end of the text to act on, in place of the region.
+
+Negative values of ARG indent backward, so you can remove all
+indentation by specifying a large negative ARG."
   (interactive "r\nP\np")
   (if (and (not arg) interactive)
       (progn
@@ -217,6 +214,48 @@ and <S-right>.")
         (forward-line 1))
       (move-marker end nil))))
 
+(defun indent-rigidly--pop-undo ()
+  (and (memq last-command '(indent-rigidly-left indent-rigidly-right
+			    indent-rigidly-left-to-tab-stop
+			    indent-rigidly-right-to-tab-stop))
+       (consp buffer-undo-list)
+       (eq (car buffer-undo-list) nil)
+       (pop buffer-undo-list)))
+
+(defun indent-rigidly-left (beg end)
+  "Indent all lines between BEG and END leftward by one space."
+  (interactive "r")
+  (indent-rigidly--pop-undo)
+  (indent-rigidly
+   beg end
+   (if (eq (current-bidi-paragraph-direction) 'right-to-left) 1 -1)))
+
+(defun indent-rigidly-right (beg end)
+  "Indent all lines between BEG and END rightward by one space."
+  (interactive "r")
+  (indent-rigidly--pop-undo)
+  (indent-rigidly
+   beg end
+   (if (eq (current-bidi-paragraph-direction) 'right-to-left) -1 1)))
+
+(defun indent-rigidly-left-to-tab-stop (beg end)
+  "Indent all lines between BEG and END leftward to a tab stop."
+  (interactive "r")
+  (indent-rigidly--pop-undo)
+  (let* ((current (indent-rigidly--current-indentation beg end))
+	 (rtl (eq (current-bidi-paragraph-direction) 'right-to-left))
+	 (next (indent--next-tab-stop current (if rtl nil 'prev))))
+    (indent-rigidly beg end (- next current))))
+
+(defun indent-rigidly-right-to-tab-stop (beg end)
+  "Indent all lines between BEG and END rightward to a tab stop."
+  (interactive "r")
+  (indent-rigidly--pop-undo)
+  (let* ((current (indent-rigidly--current-indentation beg end))
+	 (rtl (eq (current-bidi-paragraph-direction) 'right-to-left))
+	 (next (indent--next-tab-stop current (if rtl 'prev))))
+    (indent-rigidly beg end (- next current))))
+
 (defun indent-line-to (column)
   "Indent current line to COLUMN.
 This function removes or adds spaces and tabs at beginning of line