external close_document : t -> tree = "caml_xml_tree_builder_close_document"
external open_tag : t -> string -> unit = "caml_xml_tree_builder_open_tag"
external close_tag : t -> string -> unit = "caml_xml_tree_builder_close_tag"
external close_document : t -> tree = "caml_xml_tree_builder_close_document"
external open_tag : t -> string -> unit = "caml_xml_tree_builder_open_tag"
external close_tag : t -> string -> unit = "caml_xml_tree_builder_close_tag"