7.1.8 UNDO LAST

The UNDO LAST command provides a limited undo function that is capable of
reversing the action of commands that modify or delete entities. Commands
such as DRAW LINE or DRAW ARC etc. are not affected by UNDO LAST as they
create, as opposed to modify entities. As the name of the command implies,
UNDO LAST can only undo the last valid command.

When IDENTS is used to select entities in a command that will modify
entities, the previous state of any selected entities is stored in an undo
buffer. The UNDO LAST command will then restore modified entities to their
previous state if required. Commands such as VERIFY ENTITY will not affect
the undo buffer as this type of command only selects entities for reference
and not for modification.  

The list of commands that may be reversed via UNDO LAST is as follows:

   CHANGE ARC            CHANGE DEPTH          CHANGE DIMENSION
   CHANGE ELLIPSE        CHANGE FONT           CHANGE LAYER
   CHANGE POLYGON        CHANGE STRING         CHANGE SYMBOL
   CHANGE TEXT           CHANGE TNODE          CHANGE XHATCH   
   DELETE ENTITY         DRAW FILLET           EXCLUDE ENTITY
   MIRROR ENTITY         MOVE ENTITY           ROTATE ENTITY   
   SCALE ENTITY          STRETCH ENTITY        STRETCH WINDOW 
   TRIM ENTITY      

The following commands reset the undo buffer:

   DEFINE SHEET                  DELETE VIEWPORT       
   CLOSE DRAWING                 SAVE DRAWING      
   SELECT ENVIRONMENT [UNDO]     UNDO LAST

The number of entities that can be undone from modification be the last
command is limited by the size of the undo buffer. This is set as default to
64K and can be increased or decreased in size using the SELECT ENVIRONMENT
command.


   COMMAND FORMAT

      #UNDO LAST [CR]

A requester will appear for confirmation that the undo is required. Once
this is answered OK the action of UNDO LAST cannot be reversed.