RSS feed: author topic

I do not believe that is available in stock WordPress, you would need to use a plugin or create one that would let you mash up both the user AND the category in a feed.

Do you know how to even do that as a search? Or do I need to find an Advanced Search plugin?

Someone please test to see if this is correct, but a URL of the following form might work — as far as the search goes.

https://foo.org/author/multiplicity/&cat=14

where cat 14 is the category “bar”

and the RSS feed would be
feed://foo.org/author/multiplicity/&cat=14/feed

I discovered this after playing with the plugin “Search Unleashed” but I don’t think the plugin is necessary to make this work — just to make the url apparent to me.

why do you need someone to test it? You can test it yourself to see if it’s correct.