code: func (v *Expander) SetLabel(label string) {
  	var cstr *C.char
  	if label != "" {
  		cstr = C.CString(label)
  		defer C.free(unsafe.Pointer(cstr))
  	}
  	C.gtk_expander_set_label(v.native(), (*C.gchar)(cstr))
  }
docs: // SetLabel is a wrapper around gtk_expander_set_label().