I'm guessing they want to check if the action exists or not so they can call another action maybe?
It's not DoubleClick, it's Double click
. Table & field names are case sensitive. They have to be written exactly as they are inside of the editor.
Example: I have a command called left_click, now to access the action for that inside of the current object below the cursor I could do something like...
if game.CurrentObject.ObjectActions["'left_click' executed"] ~= nil then
print("does not exist")
... I have no idea if what I've just written is correct though as I'm writing off the top of my head.