question: returns a list of optional keys . concode_field_sep int RESERVED concode_elem_sep StructuredDataId ORIGIN concode_elem_sep long serialVersionUID concode_elem_sep int enterpriseNumber concode_elem_sep String AT_SIGN concode_elem_sep StructuredDataId META concode_elem_sep int MAX_LENGTH concode_elem_sep String name concode_elem_sep StructuredDataId TIME_QUALITY concode_elem_sep String[] optional concode_elem_sep String[] required concode_field_sep StructuredDataId makeId concode_elem_sep StructuredDataId makeId concode_elem_sep String getName concode_elem_sep int getEnterpriseNumber concode_elem_sep boolean isReserved concode_elem_sep String toString concode_elem_sep String[] getRequired
target: String [ ] function ( ) { return optional ; }