public List<Field> specFields () {
        List<Field> specFields = new ArrayList<>();
        for (Field f : fields) if (f.requirement == REQUIRED || f.requirement == OPTIONAL) specFields.add(f);
        return specFields;
    }
public List<Field> specFields () {
        List<Field> specFields = new ArrayList<>();
        for (Field f : fields) if (f.requirement == REQUIRED || f.requirement == OPTIONAL) specFields.add(f);
        return specFields;
    }
public List < Field > specFields ( ) { List < Field > specFields = new ArrayList <> ( ) ; for ( Field f : fields ) if ( f . requirement == REQUIRED || f . requirement == OPTIONAL ) specFields . add ( f ) ; return specFields ; }
Get only those fields included in the official GTFS specification for this table, i.e., filter out fields used
in the editor or extensions.
Get only those fields included in the official GTFS specification for this table i . e . filter out fields used in the editor or extensions .