diff -u b/core/lib/Drupal/Component/Datetime/DateTimePlus.php b/core/lib/Drupal/Component/Datetime/DateTimePlus.php
--- b/core/lib/Drupal/Component/Datetime/DateTimePlus.php
+++ b/core/lib/Drupal/Component/Datetime/DateTimePlus.php
@@ -284,7 +284,7 @@
   }
 
   /**
-   * {@inheritdoc}
+   * Passes through all unknown calls onto the DateTime object.
    */
   public function __call($method, $args) {
     // @todo consider using assert() as per https://www.drupal.org/node/2451793.
@@ -298,7 +298,7 @@
   }
 
   /**
-   * {@inheritdoc}
+   * Passes through all unknown static calls onto the DateTime object.
    */
   public static function __callStatic($method, $args) {
     if (!method_exists('\DateTime', $method)) {
@@ -308,7 +308,7 @@
   }
 
   /**
-   * {@inheritdoc}
+   * Deep-clones the DateTime object we're wrapping.
    */
   public function __clone() {
     $this->dateTimeObject = clone($this->dateTimeObject);