Как добраться до конкретного фрейма?

var

  HTML_Doc: IHTMLDocument2;
  Window: IHTMLWindow2;
  oRange1: variant;
  name_frame: OleVariant;

  HTML_Doc := WebBrowser1.Document as IHTMLDocument2;
  Window := HTML_Doc.parentWindow as IHTMLWindow2;
  name_frame := 'mainFrame';
  oRange1 := Window.frames.item(name_frame).document.body.createTextRange;