code: func (p *WebPage) SetClipRect(rect Rect) error {
  	req := map[string]interface{}{
  		"ref": p.ref.id,
  		"rect": rectJSON{
  			Top:    rect.Top,
  			Left:   rect.Left,
  			Width:  rect.Width,
  			Height: rect.Height,
  		},
  	}
  	return p.ref.process.doJSON("POST", "/webpage/SetClipRect", req, nil)
  }
docs: // SetClipRect sets the clipping rectangle used when rendering.
  // Set to nil to render the entire webpage.