code: function before_head_mode(t,value,arg3,arg4) {
      switch(t) {
      case 1: // TEXT
        value = value.replace(LEADINGWS, "");  // Ignore spaces
        if (value.length === 0) return; // Are we done?
        break;  // Handle anything non-space text below
      case 5: // DOCTYPE
        /* ignore the token */
        return;
      case 4: // COMMENT
        insertComment(value);
        return;
      case 2: // TAG
        switch(value) {
        case "html":
          in_body_mode(t,value,arg3,arg4);
          return;
        case "head":
          var elt = insertHTMLElement(value, arg3);
          head_element_pointer = elt;
          parser = in_head_mode;
          return;
        }
        break;
      case 3: // ENDTAG
        switch(value) {
        case "html":
        case "head":
        case "body":
        case "br":
          break;
        default:
          return; // ignore most end tags
        }
      }
  
      // If not handled explicitly above
      before_head_mode(TAG, "head", null); // create a head tag
      parser(t, value, arg3, arg4); // then try again with this token
    }
docs: 11.2.5.4.3 The "before head" insertion mode