7.0;undo *DM*, revision 7.0, 83/08/17
UNDO -- Undo previous DM command(s).
usage: undo
FORMAT
UNDO
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. Successive UNDOs will undo further back in history. Note
that this only applies to DM operations; Shell operations (such as compiling a
program) cannot be undone.
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 together in sets. For example, a S (SUBSTITUTE) command
may change five lines. While UNDO considers this to be five entries, the five
entries are grouped into a single set so that one UNDO will change all five
lines back to their original state. When a buffer becomes full, the oldest
set of entries is erased. This means that UNDO will never partially undo an
operation: it will either completely undo it or do 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 on low-profile keyboards invokes the UNDO command.
There is no predefined key for this function on 880 keyboards.
UNDO requires no arguments or options.