How to create a custom feed template?

Hello,

I am trying to create a custom feed on the basis of the existing feeds (wordpress/wp-[rss2|atom|rss|...].php), but I am having trouble integrating it into wordpress so as to make it available through http://example.com/?feed=myspecialfeed

I have currently simply copied the wp-rss2.php to wp-myspecialfeed.php, and found the functions do_feed_* in wp-includes/functions.php, and added my own function do_feed_myspecialfeed, but apparently this is not enough.

Could somebody please tell me what else is needed to create a custom feed? Thanks in advance,

Jakob.

http://codex.wordpress.org/Customizing_Feeds does only say

“There are a variety of ways to customize your feeds, through the use of third-party software you install and add-on to your WordPress site, or by manually changing the feed templates to meet your needs.”

which is not really illuminating 😉