Check to see if the page is from a Special Topics Provider Site (STPS), one that hosts content on many topics (such as youtube.com). If so:

1. Do not use the hostname to train the classifier
2. Check for a meta tag in the page head containing the section or channel name. Use the content of this meta tag to train the classifier instead
3. If no meta tag containing the section or channel name is found, disable Topics API on this STPS page.

Special Topics Provider Sites could enroll, using the existing enrollment process, specifying that they want to be part of the STPS program. The browser or an independent party could crawl the site and check that the site has at least "n" pages that are classified as at least "m" different topics before adding the site to the STPS list.

(simpler solution to achieve a large fraction of the benefits of #118 with less complexity and risk)