I'm not sure that I can explain it well. Reviewing some documentation as well as the script's actual
KeyHistory may be informative. The KeyHistory shows you what is happening with the keys. There, you can match the actions with the script. The
$ prefix prevents the Send command from triggering the routine again when the routine sends its own hotkey. See the
list of modifiers, including
! representing
Alt. The
blind mode mostly changes how modifier keys are handled. There again, if you examine the key history, you can see the effects with or without the blind mode.
The main idea of the script is to send the hotkey while
Alt is up, and then to keep
Alt up after that. This is essentially an
ad hoc solution, and there may be better ones.