code: function startTagInFrameset(p, token) {
      const tn = token.tagName;
  
      if (tn === $.HTML) {
          startTagInBody(p, token);
      } else if (tn === $.FRAMESET) {
          p._insertElement(token, NS.HTML);
      } else if (tn === $.FRAME) {
          p._appendElement(token, NS.HTML);
          token.ackSelfClosing = true;
      } else if (tn === $.NOFRAMES) {
          startTagInHead(p, token);
      }
  }
docs: The "in frameset" insertion mode ------------------------------------------------------------------