val next_sibling : t -> node -> node
val prev_sibling : t -> node -> node
val next_element : t -> node -> node
val tagged_sibling : t -> node -> Tag.t -> node
val next_sibling : t -> node -> node
val prev_sibling : t -> node -> node
val next_element : t -> node -> node
val tagged_sibling : t -> node -> Tag.t -> node