DateTimeFormat.format_part
method _type : Js_of_ocaml__Js.js_string Js_of_ocaml__Js.t Js_of_ocaml__Js.readonly_prop
method _value : Js_of_ocaml__Js.js_string Js_of_ocaml__Js.t Js_of_ocaml__Js.readonly_prop