Index: src/wp-includes/post.php
===================================================================
--- src/wp-includes/post.php	(revision 27134)
+++ src/wp-includes/post.php	(working copy)
@@ -4093,6 +4093,16 @@
 
 	// expected_slashed (everything!)
 	$data = compact( array( 'post_author', 'post_date', 'post_date_gmt', 'post_content', 'post_content_filtered', 'post_title', 'post_excerpt', 'post_status', 'post_type', 'comment_status', 'ping_status', 'post_password', 'post_name', 'to_ping', 'pinged', 'post_modified', 'post_modified_gmt', 'post_parent', 'menu_order', 'post_mime_type', 'guid' ) );
+
+	/**
+	 * Filter attachment post data before it is updated in or added
+	 * to the database.
+	 *
+	 * @since 3.9.0
+	 *
+	 * @param array $data   Array of sanitized attachment post data.
+	 * @param array $object Array of un-sanitized attachment post data.
+	 */
 	$data = apply_filters( 'wp_insert_attachment_data', $data, $object );
 	$data = wp_unslash( $data );