Most browsers today will automatically enable their RSS/Atom reader option when you're on a page that has a feed in it. This is because the page has one or more <link> elements pointing to RSS/Atom endpoints, for example: <link rel="alternate"...

NOTE: this post was originally published on 5/20/10 but somehow disappeared, probably during the transition to the new blogging infrastructure in blogs.msdn.com. This version should be close to the original although it may differ in details. Back when...