What is a "wantlist"?
A description of a subset can be saved as a "wantlist". A NIEM / GJXDM wantlist is an XML instance (based on a schema) for identifying the NIEM / GJXDM components required for a given subset. It is the intermediate format that the SSGT itself uses and edits, and can be persisted (saved to disk, emailed, published online, etc.) to feed the selected types and elements into the SSGT at a later time.
By employing this open XML-based specification, it is possible for other tools (such as editors or schema builders) to interact with the SSGT and to exchange subset definitions between tools.