diff -u b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
--- b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
@@ -30,6 +30,12 @@
     return $GLOBALS['base_url'] . '/' . self::getDirectoryPath() . '/' . drupal_encode_path($path);
   }
 
+  /**
+   * Returns the base path for public://
+   *
+   * @return string
+   *   the base path for public:// typically sites/default/files.
+   */
   static public function basePath() {
     $base_path = settings()->get('file_public_path', conf_path() . '/files');
     if ($test_prefix = drupal_valid_test_ua()) {