1. DomName('SVGPathSegList.insertItemBefore')
  2. DocsEditable()
PathSeg insertItemBefore(PathSeg newItem, int index)

Source 

@DomName('SVGPathSegList.insertItemBefore')
@DocsEditable()
PathSeg insertItemBefore(PathSeg newItem, int index) => _blink.BlinkSVGPathSegList.instance.insertItemBefore_Callback_2_(this, newItem, index);