code: function(conn) {
  
          this._connection = conn;
  
          /*
          Function used to setup plugin.
          */
  
          /* extend name space
          *  NS.PUBSUB - XMPP Publish Subscribe namespace
          *              from XEP 60.
          *
          *  NS.PUBSUB_SUBSCRIBE_OPTIONS - XMPP pubsub
          *                                options namespace from XEP 60.
          */
          Strophe.addNamespace('PUBSUB',"http://jabber.org/protocol/pubsub");
          Strophe.addNamespace('PUBSUB_SUBSCRIBE_OPTIONS',
                               Strophe.NS.PUBSUB+"#subscribe_options");
          Strophe.addNamespace('PUBSUB_ERRORS',Strophe.NS.PUBSUB+"#errors");
          Strophe.addNamespace('PUBSUB_EVENT',Strophe.NS.PUBSUB+"#event");
          Strophe.addNamespace('PUBSUB_OWNER',Strophe.NS.PUBSUB+"#owner");
          Strophe.addNamespace('PUBSUB_AUTO_CREATE',
                               Strophe.NS.PUBSUB+"#auto-create");
          Strophe.addNamespace('PUBSUB_PUBLISH_OPTIONS',
                               Strophe.NS.PUBSUB+"#publish-options");
          Strophe.addNamespace('PUBSUB_NODE_CONFIG',
                               Strophe.NS.PUBSUB+"#node_config");
          Strophe.addNamespace('PUBSUB_CREATE_AND_CONFIGURE',
                               Strophe.NS.PUBSUB+"#create-and-configure");
          Strophe.addNamespace('PUBSUB_SUBSCRIBE_AUTHORIZATION',
                               Strophe.NS.PUBSUB+"#subscribe_authorization");
          Strophe.addNamespace('PUBSUB_GET_PENDING',
                               Strophe.NS.PUBSUB+"#get-pending");
          Strophe.addNamespace('PUBSUB_MANAGE_SUBSCRIPTIONS',
                               Strophe.NS.PUBSUB+"#manage-subscriptions");
          Strophe.addNamespace('PUBSUB_META_DATA',
                               Strophe.NS.PUBSUB+"#meta-data");
          Strophe.addNamespace('ATOM', "http://www.w3.org/2005/Atom");
  
          if (conn.disco)
              conn.disco.addFeature(Strophe.NS.PUBSUB);
  
      }
docs: The plugin must have the init function.