sig
  type crossing_mode = NotifyNormal | NotifyGrab | NotifyUngrab
  type crossing_detail =
      NotifyAncestor
    | NotifyVirtual
    | NotifyInferior
    | NotifyNonlinear
    | NotifyNonlinearVirtual
  type crossing_state =
      Button1Mask
    | Button2Mask
    | Button3Mask
    | Button4Mask
    | Button5Mask
    | ShiftMask
    | LockMask
    | ControlMask
    | Mod1Mask
    | Mod2Mask
    | Mod3Mask
    | Mod4Mask
    | Mod5Mask
end