Form calls your user edit routine with the type parameter set to U_FKEY when the operator presses a function key not recognized by form. Form recognizes function keys F1 through F8 as its function keys. If your terminal definition defines additional function keys above F8, form calls your user edit routine each time the operator presses any function key above F8. The exit_char parameter contains the value of the key pressed, as defined in the include file \cbase\include\cbase\escape.h.
When the cursor is within a field, form considers all function keys (including function keys above F8) as a terminator for data entry. As a result, before form calls your U_FKEY user edit routine, the data in the field is validated and form calls your U_USEREDIT user edit routine, if necessary.