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.

1 files changed, 20 insertions, 8 deletions

diff --git a/doc/emacs/indent.texi b/doc/emacs/indent.texi
index 43294866b7b..0e35a63aa98 100644
--- a/doc/emacs/indent.texi
+++ b/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 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}}.
+This command is used to change the indentation of all lines that begin
+in the region, moving the affected lines as a ``rigid'' unit.
+
+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