code: function() {
      var self = this;
  
      if (self.filter.get("valid")) {
        self.$el.removeClass("invalidvalid");
        self.$el.addClass("valid");
      }
      else {
        self.$el.removeClass("valid");
        self.$el.addClass("invalid");
      }
    }
docs: Adds an 'active' class to the view element if the attribute filter is valid.
  @method setValidClass