anchor.diff:      }
       AstNode node = new NodeLocator.con1(offset).searchWithin(root);
       return node.getAncestor(predicate);
  -  }
  -
  -  /**
  -   * Calculate the offset where the given strings differ.
  -   *
  -   * @param str1 the first String to compare
  -   * @param str2 the second String to compare
  -   * @return the offset at which the strings differ (or <code>-1</code> if they do not)
  -   */
  -  static int _getDiffPos(String str1, String str2) {
  -    int len1 = math.min(str1.length, str2.length);
  -    int diffPos = -1;
  -    for (int i = 0; i < len1; i++) {
  -      if (str1.codeUnitAt(i) != str2.codeUnitAt(i)) {
  -        diffPos = i;
  -        break;
  -      }
  -    }
  -    if (diffPos == -1 && str1.length != str2.length) {
  -      diffPos = len1;
  -    }
  -    return diffPos;
     }
   
     static void _privateAssertContains(List<Object> array, List<bool> found,
  
positive.code:     }
      return object;
    }
  
    /**
     * Assert that the actual token has the same type and lexeme as the expected token. Note that this
     * does not assert anything about the offsets of the tokens (although the lengths will be equal).
     *
     * @param expectedToken the token that was expected
     * @param actualToken the token that was found
     * @throws AssertionFailedError if the two tokens are not the same
     */
    static void assertMatches(Token expectedToken, Token actualToken) {
      expect(actualToken.type, expectedToken.type);
      if (expectedToken is KeywordToken) {
        assertInstanceOf((obj) => obj is KeywordToken, KeywordToken, actualToken);
        expect((actualToken as KeywordToken).keyword, expectedToken.keyword);
      } else if (expectedToken is StringToken) {
        assertInstanceOf((obj) => obj is StringToken, StringToken, actualToken);
        expect((actualToken as StringToken).lexeme, expectedToken.lexeme);
      }
    }
  
  
    /**
     * @return the [AstNode] with requested type at offset of the "prefix".
  
negative.code:     List<bool> found = new List<bool>.filled(expectedSize, false);
      for (int i = 0; i < expectedSize; i++) {
        _privateAssertContains(array, found, expectedElements[i]);
      }
    }
  
  