docs: function (items, options) {
              options = options || {};
  
              this.$items = [];
              this.$itemEventMap = {};
  
              this.callBase(options);
  
              if (items) {
                  this.add(items);
              }
  
              var self = this;
  
              function updateLength() {
                  self.length = self.size();
              }
  
              // TODO: allow array here to give multiple event hin
              this.bind('add', updateLength);
              this.bind('remove', updateLength);
              this.bind('reset', updateLength);
  
              this.length = this.size();
          }