...where 'intro' is the _id_ of the item in the manifest you want to navigate to. This tells the SCORM 2004 API to attempt to navigate (choice navigation) to a target of 'intro' and there would have to be an existing SCO in that package with an id of 'intro' for it to work properly.
More information on Navigation Requests can be found in section 5.6.6 of the SCORM 2004 3rd edition SCORM_SeqNav.pdf file. This is only one of the many options you can trigger when a SCO closes. The available navigation requests are:
choice (with target)