`sig
val ok : [> `OK ] GWindow.buttons
val close : [> `CLOSE ] GWindow.buttons
val yes_no : [> `NO | `YES ] GWindow.buttons
val ok_cancel : [> `CANCEL | `OK ] GWindow.buttons
type color_selection = [ `CANCEL | `DELETE_EVENT | `HELP | `OK ]
type file_selection = [ `CANCEL | `DELETE_EVENT | `HELP | `OK ]
type font_selection = [ `APPLY | `CANCEL | `DELETE_EVENT | `OK ]
type about = [ `CANCEL | `CLOSE | `DELETE_EVENT ]
end`