| FIRST_CHILD of StateSet.t
| NEXT_SIBLING of StateSet.t
| FIRST_ELEMENT of StateSet.t
| NEXT_ELEMENT of StateSet.t
| TAGGED_DESCENDANT of StateSet.t * Tag.t
| TAGGED_FOLLOWING of StateSet.t * Tag.t
| FIRST_CHILD of StateSet.t
| NEXT_SIBLING of StateSet.t
| FIRST_ELEMENT of StateSet.t
| NEXT_ELEMENT of StateSet.t
| TAGGED_DESCENDANT of StateSet.t * Tag.t
| TAGGED_FOLLOWING of StateSet.t * Tag.t