Index: wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
===================================================================
--- wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	(revision 48360)
+++ wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	(working copy)
@@ -2424,7 +2424,15 @@
 		// Emit a _doing_it_wrong warning if user tries to add new properties using this filter.
 		$new_fields = array_diff( array_keys( $schema['properties'] ), $schema_fields );
 		if ( count( $new_fields ) > 0 ) {
-			_doing_it_wrong( __METHOD__, __( 'Please use register_rest_field to add new schema properties.' ), '5.4.0' );
+			_doing_it_wrong(
+				__METHOD__,
+				sprintf(
+					/* translators: %s: register_rest_field */
+					__( 'Please use %s to add new schema properties.' ),
+					'<code>register_rest_field<code>'
+				),
+				'5.4.0'
+			);
 		}
 
 		$this->schema = $schema;