README.undo

The undo in Mg3a is similar to in GUI applications. It's a linear
undo, with one undo list per buffer.


Commands:

"undo"				- An undo that initially goes backward in time. If you do
				  something else that doesn't change the buffer, it
				  switches direction from backward to forward or from
				  forward to backward. Bound to "C-x u" and "C-_".

				  Note that if you change the buffer while undone, "the
				  future" is removed.

"undo-only"			- An undo that goes only backward in time.

"redo"				- An undo that goes only forward in time.

"undo-boundary"			- Manually specify an undo boundary. Scripts are otherwise
				  undone as one unit.


Variables:

"undo-limit"			- A limit on the number of bytes in the undo-list, per-
				  buffer. This is a hard limit. Default is 1000000.

"undo-enabled"			- Controls whether undo is enabled. Default is 1.


Repeat counts:

"undo", "undo-only" and "redo" accept repeat counts. A repeat count of
0 counts as infinite.


Notes:

- Undo restores content, and the modified flag; not other buffer
  flags.

- Each step of undoing/redoing is done to the next undo boundary.

  Interactively, there is an undo boundary before each command, except
  if two sequential commands are the same and they are "self-insert-
  command", "delete-char", "delete-backward-char" or "backward-delete-
  char-untabify".

- Overhead is counted toward "undo-limit".

- #define LIST_UNDO to enable a "list-undo" command to show the undo list.