How do series/show episode scrapers work?

I’ve read the wiki pages about how to develop scraper XML:

How_To_Write_Media_Info_Scrapers (wiki)
Scraper.xml (wiki)

and I’ve made my own movies scraper, but I don’t understand how the scraper XML for series/show episodes works and I don’t see any documentation for most of the stuff I see in addons/metadata.tvdb.com/tvdb.xml.

How do series/show scrapers work? I’m going blind trying to read the C++.