anchor.diff:  
     void _createAttrMappings(directive, scope, List<MappingParts> mappings, nodeAttrs, formatters,
                              tasks) {
  +    Scope directiveScope; // Only created if there is a two-way binding in the element.
       mappings.forEach((MappingParts p) {
         var attrName = p.attrName;
         var dstExpression = p.dstExpression;
  
positive.code: 
          case '<=>': // two-way
            if (nodeAttrs[attrName] == null) return;
  
            _bindTwoWay(tasks, nodeAttrs[attrName], scope, dstPathFn,
                directive, formatters, dstExpression);
            break;
  
  
negative.code:   bool get hasDirectivesOrEvents =>
        _usableDirectiveRefs.isNotEmpty || onEvents.isNotEmpty;
  
    void _bindTwoWay(tasks, expression, scope, directiveScope,
                     dstPathFn, controller, formatters, dstExpression) {
      var taskId = tasks.registerTask();
      Expression expressionFn = _parser(expression);
  
  