The %FIELDS built-in function restricts which fields an UPDATE writes back to
the record. Without %FIELDS, all fields in the record format are updated; with it,
only the named fields are written and the remaining fields retain their on-disk values.
UPDATE INVMASTR %FIELDS(QTY:PRICE); // only QTY and PRICE are updated
UPDATE(E) SFLREC %FIELDS(OPT); // (E) and %FIELDS can coexist
Field names are colon-separated and case-insensitive. %FIELDS is free-format only;
there is no fixed-format equivalent.