code: function(models, out)
    {
      var target = out || this.cloneEmpty();
  
      for (var i = 0; i < models.length; i++)
      {
        var a = models[ i ];
        var key = this.buildKeyFromInput( a );
  
        if ( this.has( key ) )
        {
          target.push( a );
        }
      }
  
      return target;
    }
docs: Documented in Collection.js