WordPress at a glance
function is not described

wp_revisions_to_keep() WP 3.6.0

Determine how many revisions to retain for a given post.

By default, an infinite number of revisions are kept.

The constant WP_POST_REVISIONS can be set in wp-config to specify the limit of revisions to keep.

Hooks in function
Return

Int. The number of revisions to keep.

Usage

wp_revisions_to_keep( $post );
$post(WP_Post) (required)
The post object.

Code of wp revisions to keep: wp-includes/revision.php VER 5.1.1

<?php
function wp_revisions_to_keep( $post ) {
	$num = WP_POST_REVISIONS;

	if ( true === $num ) {
		$num = -1;
	} else {
		$num = intval( $num );
	}

	if ( ! post_type_supports( $post->post_type, 'revisions' ) ) {
		$num = 0;
	}

	/**
	 * Filters the number of revisions to save for the given post.
	 *
	 * Overrides the value of WP_POST_REVISIONS.
	 *
	 * @since 3.6.0
	 *
	 * @param int     $num  Number of revisions to store.
	 * @param WP_Post $post Post object.
	 */
	return (int) apply_filters( 'wp_revisions_to_keep', $num, $post );
}