https://www.zylstra.org/blog/2022/11/22577/ explaining and bookmarking:
https://diggingthedigital.com/rss-feeds-in-mastodon/
Which is in Dutch but put it through a translator or not, you get the syntax.
It is going to be really interesting to see what happens in the next two years with RSS as there ends up being that hole created by the Twitter mess. Hopefully Mastodon could take full advantage of it.
Dave Winer has been posting on Mastodon. He has an idea for 2-way RSS. We shall see.