only register undo when a value actually changes
only register undo when a value actually changes
WoLpH/skim,WoLpH/skim,WoLpH/skim,ycaihua/skim-app,ycaihua/skim-app,ycaihua/skim-app,WoLpH/skim,ycaihua/skim-app,ycaihua/skim-app,WoLpH/skim