diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -72,7 +72,7 @@
     'rsrc/css/application/differential/table-of-contents.css' => 'bba788b9',
     'rsrc/css/application/diffusion/diffusion-icons.css' => '23b31a1b',
     'rsrc/css/application/diffusion/diffusion-readme.css' => 'b68a76e4',
-    'rsrc/css/application/diffusion/diffusion-repository.css' => 'b89e8c6c',
+    'rsrc/css/application/diffusion/diffusion-repository.css' => '20cff590',
     'rsrc/css/application/diffusion/diffusion.css' => 'e46232d6',
     'rsrc/css/application/feed/feed.css' => 'd8b6e3f8',
     'rsrc/css/application/files/global-drag-and-drop.css' => '1d2713a4',
@@ -570,7 +570,7 @@
     'diffusion-css' => 'e46232d6',
     'diffusion-icons-css' => '23b31a1b',
     'diffusion-readme-css' => 'b68a76e4',
-    'diffusion-repository-css' => 'b89e8c6c',
+    'diffusion-repository-css' => '20cff590',
     'diviner-shared-css' => '4bd263b0',
     'font-fontawesome' => '3883938a',
     'font-lato' => '23631304',
diff --git a/src/applications/diffusion/controller/DiffusionBrowseController.php b/src/applications/diffusion/controller/DiffusionBrowseController.php
--- a/src/applications/diffusion/controller/DiffusionBrowseController.php
+++ b/src/applications/diffusion/controller/DiffusionBrowseController.php
@@ -190,6 +190,10 @@
           ->setRequest($request)
           ->setDiffusionRequest($drequest);
 
+        if ($engine instanceof PHUIRemarkupView) {
+          $engine->setGenerateTableOfContents(true);
+        }
+
         $corpus = $engine->newDocumentView($ref);
 
         $this->corpusButtons[] = $this->renderFileButton();
diff --git a/src/applications/files/document/PhabricatorRemarkupDocumentEngine.php b/src/applications/files/document/PhabricatorRemarkupDocumentEngine.php
--- a/src/applications/files/document/PhabricatorRemarkupDocumentEngine.php
+++ b/src/applications/files/document/PhabricatorRemarkupDocumentEngine.php
@@ -36,6 +36,7 @@
     $content = phutil_utf8ize($content);
 
     $remarkup = new PHUIRemarkupView($viewer, $content);
+    $remarkup->setGenerateTableOfContents(true);
 
     $container = phutil_tag(
       'div',
diff --git a/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php b/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php
--- a/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php
+++ b/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php
@@ -208,12 +208,12 @@
     $this->activeEngine = $engine;
 
     $encode_setting = $request->getStr('encode');
-    if (strlen($encode_setting)) {
+    if (phutil_nonempty_string($encode_setting)) {
       $engine->setEncodingConfiguration($encode_setting);
     }
 
     $highlight_setting = $request->getStr('highlight');
-    if (strlen($highlight_setting)) {
+    if (phutil_nonempty_string($highlight_setting)) {
       $engine->setHighlightingConfiguration($highlight_setting);
     }
 
diff --git a/src/infrastructure/markup/PhabricatorMarkupEngine.php b/src/infrastructure/markup/PhabricatorMarkupEngine.php
--- a/src/infrastructure/markup/PhabricatorMarkupEngine.php
+++ b/src/infrastructure/markup/PhabricatorMarkupEngine.php
@@ -459,6 +459,10 @@
         $engine = self::newMarkupEngine(array());
         $engine->setConfig('pygments.enabled', false);
         break;
+      case 'remarkupField':
+        $engine = self::newMarkupEngine(array());
+        $engine->setConfig('header.generate-toc', true);
+        break;
       default:
         throw new Exception(pht('Unknown engine ruleset: %s!', $ruleset));
     }
diff --git a/src/infrastructure/markup/PhabricatorMarkupOneOff.php b/src/infrastructure/markup/PhabricatorMarkupOneOff.php
--- a/src/infrastructure/markup/PhabricatorMarkupOneOff.php
+++ b/src/infrastructure/markup/PhabricatorMarkupOneOff.php
@@ -97,7 +97,11 @@
     if ($this->engineRuleset) {
       return PhabricatorMarkupEngine::getEngine($this->engineRuleset);
     } else if ($this->preserveLinebreaks) {
-      return PhabricatorMarkupEngine::getEngine();
+      $engine = PhabricatorMarkupEngine::getEngine();
+      if ($this->generateTableOfContents) {
+        $engine->setConfig('header.generate-toc', true);
+      }
+      return $engine;
     } else {
       return PhabricatorMarkupEngine::getEngine('nolinebreaks');
     }
@@ -115,6 +119,16 @@
     if ($this->getGenerateTableOfContents()) {
       $toc = PhutilRemarkupHeaderBlockRule::renderTableOfContents($engine);
       $this->tableOfContents = $toc;
+      $collapsible_button = phutil_tag('button',
+        array('type' => 'button', 'class' => 'collapsible'),
+        'Open Index');
+      $toc_div = phutil_tag('div',
+        array('class' => 'collapsibleContent'),
+        $toc);
+      $collapsible_js = $this->collapsibleJavascript();
+
+      $output = phutil_implode_html("\n",
+        array($collapsible_button, $toc_div, $output, $collapsible_js));
     }
 
     require_celerity_resource('phabricator-remarkup-css');
@@ -127,6 +141,27 @@
       $output);
   }
 
+  public function collapsibleJavascript() {
+    return new PhutilSafeHTML('
+<script>
+var coll = document.getElementsByClassName("collapsible");
+var i;
+
+for (i = 0; i < coll.length; i++) {
+  coll[i].addEventListener("click", function() {
+    this.classList.toggle("active");
+    var content = this.nextElementSibling;
+    if (content.style.display === "block") {
+      content.style.display = "none";
+    } else {
+      content.style.display = "block";
+    }
+  });
+}
+</script>
+    ');
+  }
+
   public function shouldUseMarkupCache($field) {
     if ($this->getDisableCache()) {
       return false;
diff --git a/src/infrastructure/markup/blockrule/PhutilRemarkupHeaderBlockRule.php b/src/infrastructure/markup/blockrule/PhutilRemarkupHeaderBlockRule.php
--- a/src/infrastructure/markup/blockrule/PhutilRemarkupHeaderBlockRule.php
+++ b/src/infrastructure/markup/blockrule/PhutilRemarkupHeaderBlockRule.php
@@ -134,7 +134,7 @@
       list($level, $name) = $info;
 
       while ($depth < $level) {
-        $toc[] = hsprintf('<ul>');
+        $toc[] = hsprintf('<ul class="remarkup-list">');
         $depth++;
       }
       while ($depth > $level) {
diff --git a/src/infrastructure/markup/remarkup/__tests__/remarkup/interpreter-test.txt b/src/infrastructure/markup/remarkup/__tests__/remarkup/interpreter-test.txt
--- a/src/infrastructure/markup/remarkup/__tests__/remarkup/interpreter-test.txt
+++ b/src/infrastructure/markup/remarkup/__tests__/remarkup/interpreter-test.txt
@@ -30,9 +30,7 @@
 Content: (content)
 Argv: (x=y)
 
-
-
-<div class="remarkup-interpreter-error">No interpreter found: phutil_fake_test_block_interpreter</div>
+<p>phutil_fake_test_block_interpreter {{{ content }}}</p>
 ~~~~~~~~~~
 Content: (content)
 Argv: (foo=bar)
@@ -53,6 +51,4 @@
 Content: (content)
 Argv: (x=y)
 
-
-
-(No interpreter found: phutil_fake_test_block_interpreter)
+phutil_fake_test_block_interpreter {{{ content }}}
diff --git a/src/infrastructure/markup/view/PHUIRemarkupView.php b/src/infrastructure/markup/view/PHUIRemarkupView.php
--- a/src/infrastructure/markup/view/PHUIRemarkupView.php
+++ b/src/infrastructure/markup/view/PHUIRemarkupView.php
@@ -85,7 +85,7 @@
 
     $content = PhabricatorMarkupEngine::renderOneObject(
       $oneoff,
-      'default',
+      'remarkupField',
       $viewer,
       $context);
 
diff --git a/webroot/rsrc/css/application/diffusion/diffusion-repository.css b/webroot/rsrc/css/application/diffusion/diffusion-repository.css
--- a/webroot/rsrc/css/application/diffusion/diffusion-repository.css
+++ b/webroot/rsrc/css/application/diffusion/diffusion-repository.css
@@ -11,3 +11,26 @@
   .diffusion-panel-header-view.phui-header-shell {
     padding: 8px 4px 8px 16px;
 }
+
+.collapsible {
+  background-color: {$blue.button.color};
+  border: none;
+  color: {$alphawhite};
+  cursor: pointer;
+  font-size: {$biggerfontsize};
+  outline: none;
+  padding: 18px;
+  text-align: left;
+  width: 100%;
+}
+
+.active, .collapsible:hover {
+  background-color: {$blue.button.hover};
+}
+
+.collapsibleContent {
+  background-color: {$lightgreybackground};
+  display: none;
+  overflow: hidden;
+  padding: 0 18px;
+}