Wording

doc/advanced.rst

@@ -915,9 +915,11 @@ It is now possible to move the runtime logic to a new
 
 .. note::
 
-    By naming the runtime with the ``Runtime`` suffix instead of ``Extension``,
-    Twig automatically tracks updates to its source file for cache invalidation.
-    Otherwise, you can implement the method ``getLastModified(): int``.
+    The extension class should implement the ``Twig\Extension\LastModifiedExtensionInterface``
+    interface to invalidate the template cache when the runtime class is modified.
+    The ``AbstractExtension`` class implements this interface and tracks the
+    runtime class if its name is the same as the extension class but ends with
+    ``Runtime`` instead of ``Extension``.
 
 Testing an Extension
 --------------------

src/Extension/LastModifiedExtensionInterface.php

@@ -17,7 +17,7 @@ interface LastModifiedExtensionInterface extends ExtensionInterface
      * Returns the last modification time of the extension for cache invalidation.
      *
      * This timestamp should be the last time the source code of the extension class
-     * and all its dependencies were modified.
+     * and all its dependencies were modified (including the Runtime class).
      */
     public function getLastModified(): int;
 }