In both RSS and Atom syndication feeds, feed entries can have anidentifier element (optional in the case of RSS, mandatory in Atomfeeds). The entry ID is supposed to be permanent and stable, no matterwhat; things that process feeds use it to know what they've seenbefore and what they haven't.

This might seem like an unimportant picky thing, except thatLiveJournal just inadvertently gave everyone reading Planet Debian aglaring example of why it's so important. (And Planet Debian is

I have an important message for web spider operators: our generosityis not unlimited. In fact, it's probably running out.

There are a lot of web spiders out there, and many of these spidersdon't seem to be offering anything for free to the public. When youcrawl to build a private index, you're building a business in part off our resources, which you are using for free, and there is verylittle in this for us. To put it plainly, such spider