2012

If you enter undo begin without undo end, using the Number option undoes
the specified number of commands but does not back up past the begin point.
If you want to go back to before the begin point, you must use the End option,
even if the set is empty. The same applies to the U command. A mark placed
by the Mark option disappears inside an UNDO group.
Mark, Back
Mark places a mark in the undo information. Back undoes all the work done
back to this mark. If you undo one operation at a time, you are informed when
you reach the mark.
You can place as many marks as necessary. Back moves back one mark at a
time, removing the mark. If no mark is found, Back displays the following
prompt:
This will undo everything. OK? <Y>: Enter y or n or press Enter
Enter y to undo all commands entered in the current session. Enter n to ignore
the Back option.
When you use the Number option to undo multiple actions, UNDO stops if
it encounters a mark.
Undocumented Command or System Variable
Quick Reference
This command or system variable is not documented in the Help system for
one of several reasons, including
■ It is obsolete, but included in the product to maintain legacy script
compatibility
■ It was included for testing purposes and has limited or no functionality
■ It is a special case of a similar, documented command and is used in the
menu or the ribbon only
■ It was included to maintain AutoCAD compatibility and has limited or no
functionality in AutoCAD LT
Use Search to find additional information about the feature in which you are
interested, and the documented commands and system variables associated
with it.
Undocumented Command or System Variable | 1285