[jmarshall]

Correct. Each <extension> tag describes an extension to some part of XBMC (or some part of another addon) that this particular addon extends. The "point" attribute is the specific part that it extends, and there may be more attributes or elements associated with that (such as the library attribute).

Music scrapers can do both artists and album scraping, thus extend 2 parts of XBMC, whereas TV or Movie scrapers extend only 1 part of XBMC.

In theory, one addon could be written that could provide data for all 4 types, though the support for that internally is not yet fully resolved - essentially it would be a bundle of individual scrapers.

In addition, all addons that users will see extend xbmc by providing information about themselves by extending the xbmc.addon.metadata point. You'll notice that addons that provide scraper libraries don't need this extension as they don't show up in the UI anywhere - they're only a dependency of other addons.

If you want further info on extensions and extension points then the c-pluff docs are useful.

Cheers,
Jonathan