atom_entry
atom_entry is fired in Atom feed entries, right before the closing </entry> tag.
This hook provides no parameters. You use this hook by having your function echo output to the browser, or by having it perform background tasks. Your functions shouldn't return, and shouldn't take any parameters
This hook is an action which means that it primarily acts as an event trigger, instead of a content filter. This is a semantic difference, but it will help you to remember what this hook does if you use it like this: add_action('atom_entry', 'your_function');
This hook was introduced in WordPress 2.0, and will not work in earlier versions.