I'm setting up some RSS so people can subscribe to articles on my site. I understand the syntax (easy enough) and I got a test RSS file up that works. What I don't get is:

A. How many articles do I keep in my RSS feed? Infinite?! Or do I set some limit, like... only keep the newest 100 articles at any given time or something?

A. With that in mind, how do I update my RSS feed, do I have my code recreate the file every time a new article is added!? That seems like a kind of messy (though possible) way to do it. Or am I supposed to be querying the database and creating the feed on the fly? But can XML even do that?

So yeah, like I said, I understand the format and I have that working, I'm just curious about the standards and how people keep their file updated.