Web Feed Reader currently supports several file formats for syndicating content, including but not limited to RSS 0.91, 1.0, and 2.0 and Atom. It has been tested with and supports all popular XML based formats, including those by Radio Userland, Blogger and Movable Type.
Web Feed Reader can only "read" what the creator of the feed has produced. Sometimes these feeds are not formed correctly. You can verify the feed at the Feed Validator.
If a feed does not validate, wait a day or so. There is a good chance the problem will correct itself.
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RSS Terms and Definitions