code: function startTagAfterHead(p, token) {
      const tn = token.tagName;
  
      if (tn === $.HTML) {
          startTagInBody(p, token);
      } else if (tn === $.BODY) {
          p._insertElement(token, NS.HTML);
          p.framesetOk = false;
          p.insertionMode = IN_BODY_MODE;
      } else if (tn === $.FRAMESET) {
          p._insertElement(token, NS.HTML);
          p.insertionMode = IN_FRAMESET_MODE;
      } else if (
          tn === $.BASE ||
          tn === $.BASEFONT ||
          tn === $.BGSOUND ||
          tn === $.LINK ||
          tn === $.META ||
          tn === $.NOFRAMES ||
          tn === $.SCRIPT ||
          tn === $.STYLE ||
          tn === $.TEMPLATE ||
          tn === $.TITLE
      ) {
          p._err(ERR.abandonedHeadElementChild);
          p.openElements.push(p.headElement);
          startTagInHead(p, token);
          p.openElements.remove(p.headElement);
      } else if (tn === $.HEAD) {
          p._err(ERR.misplacedStartTagForHeadElement);
      } else {
          tokenAfterHead(p, token);
      }
  }
docs: The "after head" insertion mode ------------------------------------------------------------------