How to convert hook_xmlsitemap_links to xmlsitemap 6.x-2.x API?

Question

While writing a test harness for a module I wrote, I discovered my implementation of hook_xmlsitemap_links wasn't actually called anymore.

The module doesn't work with nodes but gets data from sources other than Drupal and themes that. It implemented hook_xmlsitemap_links to add its urls to the sitemap.

Is there some documentation on how to replace a hook implementation with its equivalent(s) in the new 6.x-2.x API, that breaks my search-fu style?

I found it is "kinda hard to explain" and was reading the code like suggested.