code: function startTagInRow(p, token) {
      const tn = token.tagName;
  
      if (tn === $.TH || tn === $.TD) {
          p.openElements.clearBackToTableRowContext();
          p._insertElement(token, NS.HTML);
          p.insertionMode = IN_CELL_MODE;
          p.activeFormattingElements.insertMarker();
      } else if (
          tn === $.CAPTION ||
          tn === $.COL ||
          tn === $.COLGROUP ||
          tn === $.TBODY ||
          tn === $.TFOOT ||
          tn === $.THEAD ||
          tn === $.TR
      ) {
          if (p.openElements.hasInTableScope($.TR)) {
              p.openElements.clearBackToTableRowContext();
              p.openElements.pop();
              p.insertionMode = IN_TABLE_BODY_MODE;
              p._processToken(token);
          }
      } else {
          startTagInTable(p, token);
      }
  }
docs: The "in row" insertion mode ------------------------------------------------------------------