How do RSS readers read different feeds?

sorry for a silly question, (I know it is). I didn't work with RSS before and I have a question. I wrote an RSS reader for iphone whi开发者_开发技巧ch can read one particular feed, if I try to read some other feed it doesn't work properly, I have some data missing, or sometimes it even crashes. Ok, it is naturally enough, because different feeds have different date formats, different xml elements names etc. So I don't understand how all this readers where you only need to provide url parse every feed

Thank you very much))

Just make sure your app is adhering to RSS Standards

W3C has a validation tool to verify that the RSS you're consuming is good coming in.