<?php
interface RemarkupSyntaxDocumentationProvider {
    public function getDocumentation();
}

<?php

final class DummyApplication extends PhabricatorApplication {
  public function getName() {
    return pht('Dummy');
  }

  public function getRemarkupRules() {
    return array(
      new DummyRemarkup(),
    );
  }

  public function getRoutes() {
    return [];
  }
}

final class DummyObject
{
  private $id;

  public function __construct($id) {
    $this->id = $id;
  }

  public function getID() {
    return $this->id;
  }

  public function getPHID() {
    return 'PHID-DUMM-0000000000000' . $this->id;
  }

}

final class DummyRemarkup extends PhabricatorObjectRemarkupRule implements RemarkupSyntaxDocumentationProvider {
  
    protected function getObjectNamePrefix() {
      return "DUMMY";
    }
  
    protected function loadHandles(array $objects) {
      $phids = mpull($objects, 'getPHID');
  
      $result = array();
      foreach ($objects as $id => $object) {
        $handle = new PhabricatorObjectHandle();
        $handle->setPHID($object->getPHID());
        $result[$id] = $handle;

      }
      return $result;
    }
  
    protected function loadObjects(array $ids) {
      return [
        new DummyObject(0),
        new DummyObject(1),
        new DummyObject(2),
        new DummyObject(3),
        new DummyObject(4),
        new DummyObject(5)
      ];
    }
      
    public function getDocumentation() {
      return '= Dummy remarkup explanation =
Here you find some help about the DUMMY token...
';
    }

    protected function renderObjectEmbed(
      $dummyObject,
      PhabricatorObjectHandle $handle,
      $options) {
  

      return phutil_safe_html('<strong>dummy ' . $dummyObject->getId() . '</strong>');
    }
  }

diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 9287085d03..8bf1369821 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -5878,6 +5878,7 @@ phutil_register_library_map(array(
     'QueryFormattingTestCase' => 'infrastructure/storage/__tests__/QueryFormattingTestCase.php',
     'QueryFuture' => 'infrastructure/storage/future/QueryFuture.php',
     'RemarkupProcessConduitAPIMethod' => 'applications/remarkup/conduit/RemarkupProcessConduitAPIMethod.php',
+    'RemarkupSyntaxDocumentationProvider' => 'applications/diviner/interface/RemarkupSyntaxDocumentationProvider.php',
     'RemarkupValue' => 'applications/remarkup/RemarkupValue.php',
     'RepositoryConduitAPIMethod' => 'applications/repository/conduit/RepositoryConduitAPIMethod.php',
     'RepositoryQueryConduitAPIMethod' => 'applications/repository/conduit/RepositoryQueryConduitAPIMethod.php',
diff --git a/src/aphront/configuration/AphrontApplicationConfiguration.php b/src/aphront/configuration/AphrontApplicationConfiguration.php
index 3198bb9fd4..70511dbdbc 100644
--- a/src/aphront/configuration/AphrontApplicationConfiguration.php
+++ b/src/aphront/configuration/AphrontApplicationConfiguration.php
@@ -270,6 +270,9 @@ final class AphrontApplicationConfiguration
     try {
       $response = $controller->willBeginExecution();
 
+      // store viewer in static variable, so it can be used in PhabricatorEnv's static functions
+      PhabricatorEnv::setViewer($request->getViewer());
+
       if ($request->getUser() && $request->getUser()->getPHID()) {
         $access_log->setData(
           array(
diff --git a/src/applications/diviner/controller/DivinerAtomController.php b/src/applications/diviner/controller/DivinerAtomController.php
index cf29389da9..5bc320a2dd 100644
--- a/src/applications/diviner/controller/DivinerAtomController.php
+++ b/src/applications/diviner/controller/DivinerAtomController.php
@@ -106,8 +106,24 @@ final class DivinerAtomController extends DivinerController {
     }
     $engine->process();
 
+    $extraContent = '';
+    $extraTOC = [];
+
+    // if Remarkup Syntax Help page is shown, search for RemarkupSyntaxDocumentationProviders in extensions
+    if ($book_name == 'phorge' && $atom_type == 'article' && $atom_name == 'remarkup') {
+      $remarkupSyntaxDocumentationProviders = id(new PhutilClassMapQuery())
+        ->setAncestorClass('RemarkupSyntaxDocumentationProvider')
+        ->execute();
+
+      // add custom Remarkup help
+      foreach ($remarkupSyntaxDocumentationProviders as $remarkupSyntaxDocumentationProvider) {
+        $extraContent .= $remarkupSyntaxDocumentationProvider->getDocumentation(). "\r\n\r\n";
+      }
+    }
+
     if ($atom) {
-      $content = $this->renderDocumentationText($symbol, $engine);
+      // convert Remarkup to HTML and parse Table of Content items out
+      $content = $this->renderDocumentationText($symbol, $engine, $viewer, $extraContent, $extraTOC);
       $document->appendChild($content);
     }
 
@@ -117,6 +133,9 @@ final class DivinerAtomController extends DivinerController {
       PhutilRemarkupHeaderBlockRule::KEY_HEADER_TOC,
       array());
 
+    // merge default and custom table of contents
+    $toc = array_merge($toc, $extraTOC);
+
     if (!$atom) {
       $document->appendChild(
         id(new PHUIInfoView())
@@ -617,11 +636,44 @@ final class DivinerAtomController extends DivinerController {
 
   private function renderDocumentationText(
     DivinerLiveSymbol $symbol,
-    PhabricatorMarkupEngine $engine) {
+    PhabricatorMarkupEngine $engine,
+    $viewer,
+    $extraContent,
+    array &$extraTOCItems) {
 
     $field = 'default';
     $content = $engine->getOutput($symbol, $field);
 
+    if ($extraContent != '') {
+      $remarkupEngine = PhabricatorMarkupEngine::newMarkupEngine(array())
+        ->setConfig('header.generate-toc', true)
+        ->setConfig('viewer', $viewer)
+        ->setMode(PhutilRemarkupEngine::MODE_HTML_MAIL);
+
+      try {
+        $extraContent = $remarkupEngine->markupText($extraContent);
+
+        $dom = new DOMDocument();
+        @$dom->loadHTML($extraContent);
+        $xpath = new DOMXPath($dom);
+        $headers = $xpath->query('//h1 | //h2 | //h3 | //h4 | //h5 | //h6');
+
+        foreach ($headers as $header) {
+          $key = $header->getElementsByTagName('a')->item(0)->getAttribute('name');
+          $headerDepth = (int)(substr($header->tagName, 1,1));
+          $textContent = trim($header->nodeValue);
+
+          $extraTOCItems[$key] = array(
+            $headerDepth,
+            new PhutilSafeHTML($textContent)
+          );
+        }
+      } catch (Exception $ex) {
+      }
+    }
+
+    $content->appendHTML($extraContent);
+
     if (strlen(trim($symbol->getMarkupText($field)))) {
       $content = phutil_tag(
         'div',
diff --git a/src/infrastructure/env/PhabricatorEnv.php b/src/infrastructure/env/PhabricatorEnv.php
index a471874e43..18a52ac756 100644
--- a/src/infrastructure/env/PhabricatorEnv.php
+++ b/src/infrastructure/env/PhabricatorEnv.php
@@ -58,6 +58,7 @@ final class PhabricatorEnv extends Phobject {
   private static $localeCode;
   private static $readOnly;
   private static $readOnlyReason;
+  private static $viewer;
 
   const READONLY_CONFIG = 'config';
   const READONLY_UNREACHABLE = 'unreachable';
@@ -494,9 +495,26 @@ final class PhabricatorEnv extends Phobject {
       'jump' => true,
     );
 
-    $uri = new PhutilURI(
-      'https://we.phorge.it/diviner/find/',
-      $params);
+    $useRemoteDocumentation = true;
+    if (PhabricatorEnv::$viewer) {
+      $books = id(new DivinerBookQuery())
+      ->setViewer(PhabricatorEnv::$viewer)
+      ->execute();
+
+      if (!!$books) {
+        $useRemoteDocumentation = false;
+      }
+    }
+
+    if ($useRemoteDocumentation) {
+      $uri = new PhutilURI(
+        'https://we.phorge.it/diviner/find/',
+        $params);
+    } else {
+      $uri = new PhutilURI(
+        '/diviner/find/',
+        $params);
+    }
 
     return phutil_string_cast($uri);
   }
@@ -986,5 +1004,8 @@ final class PhabricatorEnv extends Phobject {
     return $root.'/support/empty/';
   }
 
-
+  public static function setViewer($viewer)
+  {
+    PhabricatorEnv::$viewer = $viewer;
+  }
 }