phpcs.xml                                    | 6 ++++++
 tests/src/Unit/File/FileUrlGeneratorTest.php | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/phpcs.xml b/phpcs.xml
index f8e2dfe..c80909a 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -19,4 +19,10 @@
         <exclude-pattern>*Controller.php</exclude-pattern>
         <exclude-pattern>*Subscriber.php</exclude-pattern>
     </rule>
+
+    <!-- Don't require boilerplate variable docs for particular kinds of classes. -->
+    <rule name="Drupal.Commenting.VariableComment.Missing">
+        <exclude-pattern>*Constraint.php</exclude-pattern>
+        <exclude-pattern>*Subscriber.php</exclude-pattern>
+    </rule>
 </ruleset>
diff --git a/tests/src/Unit/File/FileUrlGeneratorTest.php b/tests/src/Unit/File/FileUrlGeneratorTest.php
index d752dab..107d4f7 100644
--- a/tests/src/Unit/File/FileUrlGeneratorTest.php
+++ b/tests/src/Unit/File/FileUrlGeneratorTest.php
@@ -23,6 +23,11 @@ use Symfony\Component\HttpFoundation\RequestStack;
  */
 class FileUrlGeneratorTest extends UnitTestCase {
 
+  /**
+   * The private key to use in tests.
+   *
+   * @var string
+   */
   protected static $privateKey = 'super secret key that really is just some string';
 
   /**