code: func (w *Window) Clear(x, y, width, height int) {
  	xproto.ClearArea(w.X.Conn(), false, w.Id,
  		int16(x), int16(y), uint16(width), uint16(height))
  }
docs: // Clear paints the region of the window specified with the corresponding
  // background pixmap. If the window doesn't have a background pixmap,
  // this has no effect.
  // If width/height is 0, then it is set to the width/height of the background
  // pixmap minus x/y.