Return Code	Significance
0	no error
1	zero pointer
2	function name not in userexit list

The pre_field-userexit is invoked after the field has been left with the write cursor.

Any required application parameters must be passed together with the name of the userexit in *xaf. In order to delete an userexit already set, you must pass an empty string.

The function automatically invoke any set mask listener function.