1. DomName('HTMLSelectElement.add')
  2. DocsEditable()
  3. Experimental()
void add(HtmlElement element, int before)

Source 

@DomName('HTMLSelectElement.add')
@DocsEditable()
@Experimental() // untriaged
void add(HtmlElement element, int before) => _blink.BlinkHTMLSelectElement.instance.add_Callback_2_(unwrap_jso(this), unwrap_jso(element), before);