10.0;undo *DM*, revision 1.0, 87/12/23
undo undo previous DM command(s)
usage: undo
DESCRIPTION
undo works by compiling a history of DM activities in input and edit pads
in reverse chronological order. Invoking undo reverses the effect of the
most recent DM command. Use successive undos to undo earlier commands.
Note that this applies only to DM operations; you cannot undo shell
operations, for example, compiling a program.
The undo buffers (one per edit pad and one per input pad) are circular
lists that when full, eliminate the oldest entries to make room for new
ones. Entries are grouped in sets. For example, an s (substitute)
command may change five lines. While undo considers this to be five
entries, the entries are grouped into a single set so that one undo
changes all five lines back to their original state. When a buffer
becomes full, the oldest set of entries is erased. This means that undo
never partially undoes an operation: it either completely undoes the
operation or does nothing.
An edit undo buffer can hold up to 1024 entries. An input undo buffer
can hold up to 128 entries.
By default, the UNDO key invokes the undo command.
undo requires no arguments or options.