I have an existing custom feed using do_feed_* but I see there is an undocumented (and existing since 2.1) *_add_feed. Is one better than the other?
I have do_feed_* working but since I upgraded to 3.0 last week, any URL with “&author=” in it redirects to the root site page. Take it out and it loads the page fine (but of course does not show the proper author). So, as I investigate, I wonder if *_add_feed might be better?
Relying on an undocumented method in any API is more dangerous than figuring out how to properly use a documented method.
add_feedis the best starting point and is now a documented part of WordPress. This function has been in WordPress since v2.1.You should prefer adding your custom feed using
add_feedoverdo_feed_*. An example of how to add your own custom RSS feed to WordPress is discussed on the WordPress Answers site: Cannot get add_feed to work.