diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/style/Grid.php b/core/modules/views/lib/Drupal/views/Plugin/views/style/Grid.php
index fc764de..3d00549 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/style/Grid.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/style/Grid.php
@@ -106,6 +106,14 @@ public function buildOptionsForm(&$form, &$form_state) {
 
   /**
    * Return the token-replaced row or column classes for the specified result.
+   *
+   * @param int $result_index
+   *   The delta of the result item to get custom classes for.
+   * @param string $type
+   *   The type of custom grid class to return, either "row" or "col".
+   *
+   * @return string
+   *   A space-delimited string of classes.
    */
   public function getCustomClass($result_index, $type) {
     $class = $this->options[$type . '_class_custom'];