Make String.startsWith take an optional start index.

sdk/lib/core/string.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.core;
 
 /**
  * The String class represents sequences of characters. Strings are
  * immutable. A string is represented by a sequence of Unicode UTF-16
  * code units accessible through the [codeUnitAt] or the
@@ skipping 88 matching lines @@
    */
   bool operator ==(var other);
 
   /**
    * Returns whether this string ends with [other].
    */
   bool endsWith(String other);
 
   /**
    * Returns whether this string starts with a match of [pattern].
+   *
+   * If [index] is provided, instead check if the substring starting

[floitsch, 2013/06/17 16:07:15]

If [index] is provided, checks if `this` starts with [pattern] at position
[index].

Give example with Regexp that has "^".

+   * at that index starts with [pattern].
+   *
+   * It is an error if [index] is negative or greater than [length].
    */
-  bool startsWith(Pattern pattern);
+  bool startsWith(Pattern pattern, [int index = 0]);
 
   /**
    * Returns the first position of a match of [pattern] in this string,
    * starting at [start] (inclusive).
    *
    * Returns -1 if a match could not be found.
    *
    * It is an error if start is negative or greater than [length].
    */
   int indexOf(Pattern pattern, [int start]);
@@ skipping 351 matching lines @@
         _position = position - 1;
         _currentCodePoint = _combineSurrogatePair(prevCodeUnit, codeUnit);
         return true;
       }
     }
     _position = position;
     _currentCodePoint = codeUnit;
     return true;
   }
 }