index = inGameUIAddEventHandler [handlerName, code];
inGameUIAddEventHandler [handlerName,index];
see https://community.bistudio.com/wiki/inGameUISetEventHandler
index = inGameUIAddEventHandler [handlerName, code];
inGameUIAddEventHandler [handlerName,index];
see https://community.bistudio.com/wiki/inGameUISetEventHandler
It would be convenient to have this, since inGameUISetEventHandler is the best/only way to detect the use of action menu actions, and not being stackable means it's not very safe to use.
Indeed this would be useful. Code that returns TRUE should also interrupt default action just like current command does.