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.