to a field; its job is to bundle these into an allocated argument-block
object which can later be passed to validation predicated. The other two
hook arguments should copy and free argument-block structures. They will
-be used by the forms-driver code.
+be used by the forms-driver code. You must supply the \fImak_arg\fR function,
+the other two are optional, you may supply NULL for them. In this case it
+is assumed, that \fImak_arg\fR doesn't allocate memory but simply loads the
+argument into a single scalar value.
The form driver requests \fBREQ_NEXT_CHOICE\fR and \fBREQ_PREV_CHOICE\fR assume
that the possible values of a field form an ordered set, and provide the forms