Returns a non-zero number if the specified label exists in the script.
TrueOrFalse := IsLabel(LabelName)
The name of a subroutine, hotkey, or hotstring (do not include the trailing colon(s) in LabelName).
This function returns a non-zero number if LabelName exists in the script.
This function is useful to avoid runtime errors when specifying a dynamic label in commands such as Gosub, Hotkey, Menu, and Gui.
Reports "Subroutine exists" because the subroutine does exist.
if IsLabel("Label") MsgBox, Subroutine exists else MsgBox, Subroutine doesn't exist Label: return