alt Hacker NewsI was looking at the RSS spec a while back to figure out how the category field was supposed to work and ended up digging up web directory history.
https://alexsci.com/blog/rss-categories/
Syndic8, DMOZ, NewsIsFree, and TX (lost to history?) used the same taxonomy approach seen on ooh.directory. All are defunct now, but DMOZ appears to live on as curlie.
https://en.wikipedia.org/wiki/List_of_web_directories
Technically, we could tag our RSS feeds with the taxonomy defined by ooh.dir, which would allow us to automatically sort blogs into topic groups, but I haven't found a single feed that uses the approach. We end up with ad-hoc category labels that are challenging to deduplicate, or more often, uncategorized blogs.
Taxonomy labels are often deduplicated on Wikidata, the unofficial "hub" of the modern Semantic Web. There's already a defined property for matching DMOZ/Curlie labels, and others could be added if relevant.