.NET Framework 4.6 and 4.5
Locks the most recent undo unit of the undo stack of the application. This prevents the locked unit from being merged with undo units that are added subsequently.
Public Sub LockCurrentUndoUnit
Call this method when a non-text undo unit is added to the application's main undo stack. This prevents the locked unit from being merged with undo units that are added subsequently.
Supported in: 4.6, 4.5, 4, 3.5, 3.0
.NET Framework Client Profile
Supported in: 4, 3.5 SP1