CharacterData.substringData() arguments should be mandatory

Source/core/dom/CharacterData.idl

 /*
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 interface CharacterData : Node {
 
     [TreatNullAs=NullString] attribute DOMString data;
 
     readonly attribute unsigned long length;
 
-    [TreatReturnedNullStringAs=Null, RaisesException] DOMString substringData([Default=Undefined] optional unsigned long offset, [IsIndex,Default=Undefined] optional unsigned long length);
+    [TreatReturnedNullStringAs=Null, RaisesException] DOMString substringData(unsigned long offset, unsigned long length);
 
     void appendData(DOMString data);
     [RaisesException] void insertData(unsigned long offset, DOMString data);
     [RaisesException] void deleteData(unsigned long offset, unsigned long length);
     [RaisesException] void replaceData(unsigned long offset, unsigned long length, DOMString data);
 };
 
 CharacterData implements ChildNode;