+val map: ('a -> 'b) -> 'a box -> 'b box
+
+(*
+val document_of_box :
+ ~obj2xml:('a -> Xml.token Stream.t) -> 'a box -> Xml.token Stream.t
+*)
+
+val b_h: attr -> 'expr box list -> 'expr box
+val b_v: attr -> 'expr box list -> 'expr box
+val b_text: attr -> string -> 'expr box
+val b_object: 'expr -> 'expr box
+val b_indent: 'expr box -> 'expr box
+val b_space: 'expr box
+val b_kw: string -> 'expr box