Form calls the user edit routine with the type parameter equal
to U_NEXTFORM every time form proceeds to the next form in the
formfile or when the user pushes the NEXTFORM key. The old_value
parameter points to the name of the current form, and the new_value parameter
points to the name of the next form. The other parameters are NULL. If
an error message is returned, the new form is not displayed and the error message
is displayed on the screen.