diff --git a/packages/block-library/src/comments/index.php b/packages/block-library/src/comments/index.php
index 69044c081c74e0..f26c43501a2e9e 100644
--- a/packages/block-library/src/comments/index.php
+++ b/packages/block-library/src/comments/index.php
@@ -213,6 +213,7 @@ function register_legacy_post_comments_block() {
 	 * like `_wp_multiple_block_styles`, which is required in this case because
 	 * the block has multiple styles.
 	 */
+	/** This filter is documented in wp-includes/blocks.php */
 	$metadata = apply_filters( 'block_type_metadata', $metadata );
 
 	register_block_type( 'core/post-comments', $metadata );