anchor.diff:            "Exception caught while traversing an AST structure.",
             new CaughtException(exception, stackTrace));
       }
  +    // Found a child.
  +    if (_foundNode != null) {
  +      return null;
  +    }
  +    // Check this node.
       if (start <= _startOffset && _endOffset <= end) {
         _foundNode = node;
  -      throw new NodeLocator_NodeFoundException();
       }
       return null;
     }
  
positive.code:     if (start > _endOffset) {
        return null;
      }
      try {
        node.visitChildren(this);
      } on NodeLocator_NodeFoundException {
        rethrow;
      } catch (exception, stackTrace) {
        // Ignore the exception and proceed in order to visit the rest of the
        // structure.
  
negative.code:     if (start > _endOffset) {
        return null;
      }
      // Check children.
      try {
        node.visitChildren(this);
      } catch (exception, stackTrace) {
        // Ignore the exception and proceed in order to visit the rest of the
        // structure.
  