docs: function(vars, slot, getter) {
              if (!Array.isArray(vars)) {
                  vars = [vars];
              }
              if (vars.length == 0) return null;
              if (typeof slot === 'string') {
                  slot = this[slot];
              }
              if (typeof getter === 'undefined') {
                  getter = function() {
                      return this.data(vars[0]);
                  };
              }
              var listener = {
                  obj: this,
                  slot: slot,
                  getter: getter
              };
              vars.forEach(
                  function(name) {
                      var data = this.findDataBinding(name);
                      data[1].push(listener);
                  }, this
              );
              return listener;
          }