The
highlighted function is used to determine whether a field,
field_name, is on the path (green) in system-controlled mode, or has been passed through (green or yellow) either directly or by skips in operator-controlled mode. This can be used to determine whether an item has been entered or skipped because of logic in system-controlled mode, or whether it is before or after the high water mark in operator-controlled mode.
The function returns 1 (true) if the field has been passed (green or yellow) and 0 (false) if the field is yet to be entered (white).