<null>

Restores last bookmark stack status and enables redo.  This only works if UndoMode is enabled (see UNDO ON).

ON

Enables UNDO/REDO and bookmarkers

OFF

Disables UNDO/REDO and bookmarkers, whilst cleaning the backup buffers.

SKIP=<f_range>

Fragment range which should be ignored in any UNDO process.
It is possible to use the UNDO command to specify a fragment-range to indicate which fragments are to be ignored during the "undo" process i.e.
UNDO SKIP=8,20\25,100
This functionality is very useful to minimize the quantity of data transferred in and out during UNDO and REDO process. It is also useful when part of the geometry cannot be replaced (that is "removed and re-created") because the item IDs have to be kept without changes.

<n>

Define the number of bookmarks which to undo. UNDO 3 would be the equivalent of UNDO;UNDO;UNDO

INDEX=ON|OFF

INDEX=ON|OFF enables or disables the restore of the indices when undoing a saved state. The default is INDEX=ON, which means that the indices are restored. (Introduced 12.3.3)

Example:

UNDO ON

...

BOOKMARK

...

UNDO INDEX=OFF

UNDO

PAUSE

The  PAUSE primer will suspend the undo mechanism in order to facilitate handling of critical situations. The undo function may be reactivated using the AWAKE primer. (Introduced v12.4.2)

AWAKE

The  AWAKE primer will reactivates the undo mechanism after an earlier PAUSE primer has been issued. (Introduced v12.4.2)