Where is the code that specifics RSS feeds?

I have a custom RSS feed that I need to edit, and I can’t for the life of me find out WHERE the code for it is… It is accessed with the following URI:

/excerpt-feed

Yet I don’t see anything in .htaccess about it, and nothing in the WP settings. I have done a global search on all files for excerpt_feed with no success. I read that add_feed is used to add feeds and the only instance I find is the actual function definition.

Now one thing I will note is I ran across this thread:

https://wordpress.org/support/topic/where-is-the-code-for-my-rss-feeds

The guy was asking a very simple question to which no answer was given, then when he was frustrated he was told he was being a jerk. While I will not speculate as to how people were ‘being’ (there’s no way to know) it is unhelpful when a person’s question is not answered, then the support topic is closed without the question being answered.

I cannot tell you how many times I’ve found topics like this here (and many other forums).

What I’m looking for right now is just the answer to the question of “Where is the code for WordPress RSS feeds?”

I see the wp-rss.php and such but it’s a super short file with a redirect in it to a rss_url. The meat of the code must be elsewhere.

If the answer to that question doesn’t help then I will refine the question but please tell me that or point me to the right direction. Thank You. 🙂