First defined in: FKiSS3
		
		The letcatch action sets the value of variable to number of
		the object currently being dragged by the user.
		If no object is being dragged, variable is set to -1.
		letcatch is used in the following events:
			
		 
		variable
		variable must be a variable name.
    Example:
    ;@ letcatch(C) ; Set variable C to the number of the object currently being dragged.