type 'a t = 'a Eliom_content_core.Xml_wed.W.ttype ('a, 'b) ft = ('a, 'b) Eliom_content_core.Xml_wed.W.ftval fmap : ('a, 'b) ft -> 'a t -> 'b ttype 'a tlist = 'a Eliom_content_core.Xml_wed.W.tlistval nil : unit -> 'a tlistval singleton : 'a t -> 'a tlist