code: func (v *Clipboard) WaitForContents(target gdk.Atom) (*SelectionData, error) {
  	c := C.gtk_clipboard_wait_for_contents(v.native(), C.GdkAtom(unsafe.Pointer(target)))
  	if c == nil {
  		return nil, nilPtrErr
  	}
  	p := &SelectionData{c}
  	runtime.SetFinalizer(p, (*SelectionData).free)
  	return p, nil
  }
docs: // WaitForContents is a wrapper around gtk_clipboard_wait_for_contents