docs: function(subscriptions){
        if (subscriptions) _.extend(this.subscriptions || {}, subscriptions);
        subscriptions = subscriptions || this.subscriptions;
        if (!subscriptions || _.isEmpty(subscriptions)) return;
        // Just to be sure we don't set duplicate
        this.unsetSubscriptions(subscriptions);
  
        _.each(subscriptions, function(subscription, channel){
          var once;
          if (subscription.$once) {
            subscription = subscription.$once;
            once = true;
          }
          if (_.isString(subscription)) {
            subscription = this[subscription];
          }
          Backbone.Mediator.subscribe(channel, subscription, this, once);
        }, this);
      }