diff --git a/code/Controllers/ContentController.php b/code/Controllers/ContentController.php
index d4c6ca5640..d4e97740c7 100644
--- a/code/Controllers/ContentController.php
+++ b/code/Controllers/ContentController.php
@@ -45,11 +45,12 @@
  * Subclasses of ContentController are generally instantiated by ModelAsController; this will create
  * a controller based on the URLSegment action variable, by looking in the SiteTree table.
  *
+ * @template T of SiteTree
  */
 class ContentController extends Controller
 {
     /**
-     * @var SiteTree
+     * @var T
      */
     protected $dataRecord;
 
@@ -71,7 +72,7 @@ class ContentController extends Controller
      * The ContentController will take the URLSegment parameter from the URL and use that to look
      * up a SiteTree record.
      *
-     * @param SiteTree $dataRecord
+     * @param T|null $dataRecord
      */
     public function __construct($dataRecord = null)
     {
@@ -110,7 +111,7 @@ public function Link($action = null)
      * Return the children of a given page. The parent reference can either be a page link or an ID.
      *
      * @param string|int $parentRef
-     * @return SS_List
+     * @return SS_List<SiteTree>
      */
     public function ChildrenOf($parentRef)
     {
@@ -188,7 +189,7 @@ protected function init()
      */
     public function handleRequest(HTTPRequest $request): HTTPResponse
     {
-        /** @var SiteTree $child */
+        /** @var SiteTree|null $child */
         $child = null;
         $action = $request->param('Action');
 
@@ -243,6 +244,7 @@ public function project()
 
     /**
      * Returns the associated database record
+     * @return T
      */
     public function data()
     {
@@ -254,7 +256,7 @@ public function data()
     /**
      * Returns a fixed navigation menu of the given level.
      * @param int $level Menu level to return.
-     * @return ArrayList
+     * @return ArrayList<SiteTree>
      */
     public function getMenu($level = 1)
     {
@@ -294,6 +296,9 @@ public function getMenu($level = 1)
         return new ArrayList($visible);
     }
 
+    /**
+     * @return ArrayList<SiteTree>
+     */
     public function Menu($level)
     {
         return $this->getMenu($level);
diff --git a/code/Controllers/LeftAndMainBatchActionsExtension.php b/code/Controllers/LeftAndMainBatchActionsExtension.php
index 8e582972e3..5e6294219b 100644
--- a/code/Controllers/LeftAndMainBatchActionsExtension.php
+++ b/code/Controllers/LeftAndMainBatchActionsExtension.php
@@ -2,9 +2,13 @@
 
 namespace SilverStripe\CMS\Controllers;
 
+use SilverStripe\Admin\LeftAndMain;
 use SilverStripe\CMS\Controllers\CMSMain;
 use SilverStripe\Core\Extension;
 
+/**
+ * @extends Extension<LeftAndMain>
+ */
 class LeftAndMainBatchActionsExtension extends Extension
 {
     public function updateBatchActionsForm(&$form)
diff --git a/code/Controllers/LeftAndMainPageIconsExtension.php b/code/Controllers/LeftAndMainPageIconsExtension.php
index a735965419..e962322f06 100644
--- a/code/Controllers/LeftAndMainPageIconsExtension.php
+++ b/code/Controllers/LeftAndMainPageIconsExtension.php
@@ -5,6 +5,7 @@
 use Psr\SimpleCache\CacheInterface;
 use Psr\SimpleCache\InvalidArgumentException;
 use ReflectionException;
+use SilverStripe\Admin\LeftAndMain;
 use SilverStripe\CMS\Model\SiteTree;
 use SilverStripe\Core\ClassInfo;
 use SilverStripe\Core\Config\Config;
@@ -16,10 +17,11 @@
 
 /**
  * Extension to include custom page icons
+ *
+ * @extends Extension<LeftAndMain>
  */
 class LeftAndMainPageIconsExtension extends Extension implements Flushable
 {
-
     /**
      * @throws InvalidArgumentException
      * @throws ReflectionException
diff --git a/code/Controllers/OldPageRedirector.php b/code/Controllers/OldPageRedirector.php
index 0ff0de6095..227790388a 100644
--- a/code/Controllers/OldPageRedirector.php
+++ b/code/Controllers/OldPageRedirector.php
@@ -10,9 +10,11 @@
 use SilverStripe\Control\HTTPResponse_Exception;
 use SilverStripe\Core\Extension;
 
+/**
+ * @extends Extension<Controller>
+ */
 class OldPageRedirector extends Extension
 {
-
     /**
      * On every URL that generates a 404, we'll capture it here and see if we can
      * find an old URL that it should be redirecting to.
diff --git a/code/Forms/InternalLinkModalExtension.php b/code/Forms/InternalLinkModalExtension.php
index 069de9064e..071c2efb27 100644
--- a/code/Forms/InternalLinkModalExtension.php
+++ b/code/Forms/InternalLinkModalExtension.php
@@ -9,7 +9,8 @@
 
 /**
  * Decorates ModalController with insert internal link
- * @see ModalController
+ *
+ * @extends Extension<ModalController>
  */
 class InternalLinkModalExtension extends Extension
 {
@@ -22,17 +23,6 @@ class InternalLinkModalExtension extends Extension
         'editorAnchorLink',
     ];
 
-    /**
-     * @return ModalController
-     */
-    public function getOwner()
-    {
-        /** @var ModalController $owner */
-        $owner = $this->owner;
-        return $owner;
-    }
-
-
     /**
      * Form for inserting internal link pages
      *
diff --git a/code/Model/RedirectorPageController.php b/code/Model/RedirectorPageController.php
index 51dce80d47..79d1446bac 100644
--- a/code/Model/RedirectorPageController.php
+++ b/code/Model/RedirectorPageController.php
@@ -7,6 +7,8 @@
 
 /**
  * Controller for the {@link RedirectorPage}.
+ *
+ * @extends PageController<RedirectorPage>
  */
 class RedirectorPageController extends PageController
 {
@@ -26,7 +28,6 @@ class RedirectorPageController extends PageController
      */
     public function index(HTTPRequest $request)
     {
-        /** @var RedirectorPage $page */
         $page = $this->data();
 
         // Redirect if we can
diff --git a/code/Model/SiteTree.php b/code/Model/SiteTree.php
index f8e2b9d19c..f455ca4eff 100755
--- a/code/Model/SiteTree.php
+++ b/code/Model/SiteTree.php
@@ -1966,7 +1966,7 @@ public function getLiveURLSegment()
     /**
      * Get the back-link tracking objects that link to this page
      *
-     * @return ArrayList|DataObject[]
+     * @return ArrayList<DataObject>
      */
     public function BackLinkTracking()
     {
@@ -2007,7 +2007,7 @@ public function BackLinkTracking()
      * Returns the pages that depend on this page. This includes virtual pages, pages that link to it, etc.
      *
      * @param bool $includeVirtuals Set to false to exlcude virtual pages.
-     * @return ArrayList|SiteTree[]
+     * @return ArrayList<SiteTree>
      */
     public function DependentPages($includeVirtuals = true)
     {
@@ -2057,7 +2057,7 @@ public function DependentPages($includeVirtuals = true)
     /**
      * Return all virtual pages that link to this page.
      *
-     * @return DataList
+     * @return DataList<SiteTree>
      */
     public function VirtualPages()
     {
diff --git a/code/Model/SiteTreeExtension.php b/code/Model/SiteTreeExtension.php
index dd1cfab272..e1b73a5c6e 100644
--- a/code/Model/SiteTreeExtension.php
+++ b/code/Model/SiteTreeExtension.php
@@ -7,6 +7,9 @@
 
 /**
  * Plug-ins for additional functionality in your SiteTree classes.
+ *
+ * @template T of SiteTree
+ * @extends DataExtension<T>
  */
 abstract class SiteTreeExtension extends DataExtension
 {
diff --git a/code/Model/SiteTreeLinkTracking.php b/code/Model/SiteTreeLinkTracking.php
index 15283596b2..8adb8aa9d6 100644
--- a/code/Model/SiteTreeLinkTracking.php
+++ b/code/Model/SiteTreeLinkTracking.php
@@ -28,6 +28,8 @@
  *
  * @property DataObject|SiteTreeLinkTracking $owner
  * @method ManyManyThroughList<SiteTree> LinkTracking()
+ *
+ * @extends DataExtension<DataObject>
  */
 class SiteTreeLinkTracking extends DataExtension
 {
diff --git a/code/Search/ContentControllerSearchExtension.php b/code/Search/ContentControllerSearchExtension.php
index 64091f17d2..6cfae5a86c 100644
--- a/code/Search/ContentControllerSearchExtension.php
+++ b/code/Search/ContentControllerSearchExtension.php
@@ -2,6 +2,7 @@
 
 namespace SilverStripe\CMS\Search;
 
+use SilverStripe\CMS\Controllers\ContentController;
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Core\Extension;
 use SilverStripe\Forms\TextField;
@@ -12,6 +13,8 @@
 
 /**
  * Extension to provide a search interface when applied to ContentController
+ *
+ * @extends Extension<ContentController>
  */
 class ContentControllerSearchExtension extends Extension
 {