WordPress at a glance
function is not described

the_content_feed() WP 2.9.0

Display the post content for feeds.

No Hooks.

Return

Nothing (null).

Usage

the_content_feed( $feed_type );
$feed_type(string)
The type of feed. rss2 | atom | rss | rdf
Default: null

Code of the content feed: wp-includes/feed.php WP 5.2.2

<?php
function the_content_feed( $feed_type = null ) {
	echo get_the_content_feed( $feed_type );
}