inline uint32_t num_tags() const;
inline uint32_t subtree_size(node_t) const;
inline uint32_t subtree_tags(node_t, tag_t) const;
inline uint32_t num_tags() const;
inline uint32_t subtree_size(node_t) const;
inline uint32_t subtree_tags(node_t, tag_t) const;