code: function(to) {
              to.listenTo(this, "add", function(model) {
                  this.add(model);
              });
              to.listenTo(this, "remove", function(model) {
                  this.remove(model);
              });
              to.listenTo(this, "reset", function(colleciton, options) {
                  _.each(options.previousModels, function(model) {
                      this.remove(model);
                  }, this);
                  collection.each(function(model) {
                      this.add(model);
                  }, this);
              });
  
              this.each(function(model) {
                  to.add(model);
              });
          }
docs: Pipe this collection into another one: all the models from this collection
  will always also be in the other collection
  
  @method pipe
  @param {Collection} to collection to pipe to
  @chainable