diff -u b/core/modules/help_topics/help_topics.module b/core/modules/help_topics/help_topics.module
--- b/core/modules/help_topics/help_topics.module
+++ b/core/modules/help_topics/help_topics.module
@@ -22,7 +22,7 @@
       $output .= '<dt>' . t('Viewing help topics') . '</dt>';
       $output .= '<dd>' . t('The top-level help topics are listed on the main <a href=":help_page">Help page</a>. Links to other topics, including non-top-level help topics, can be found under the "Related" heading when viewing a topic page.', [':help_page' => Url::fromRoute('help.main')->toString()]) . '</dd>';
       $output .= '<dt>' . t('Providing help topics') . '</dt>';
-      $output .= '<dd>' . t("Modules and themes can provide help topics as YAML-file-based plugins in a project sub-directory called <em>help_topics</em>. The content of the topic is contained in a matching Twig file in <em>help_topics/templates</em>. Any file in a module or theme's <em>help_topics</em> directory with the suffix <em>*.help_topic.yml</em> will be discovered by the Help Topic module. Plugin-based help topics provided by modules and themes will automatically be updated when a module or theme is updated. Use the plugins in <em>core/modules/help_topics/help_topics</em> as a guide when writing and formatting a help topic plugin for your theme or module.") . '</dd>';
+      $output .= '<dd>' . t("Modules and themes can provide help topics as Twig-file-based plugins in a project sub-directory called <em>help_topics</em>. Plugin-based help topics provided by modules and themes will automatically be updated when a module or theme is updated. Use the plugins in <em>core/modules/help_topics/help_topics</em> as a guide when writing and formatting a help topic plugin for your theme or module.") . '</dd>';
       $output .= '<dt>' . t('Translating help topics') . '</dt>';
       $output .= '<dd>' . t('The title and body text of help topics provided by contributed modules and themes are translatable using the <a href=":locale_help">Interface Translation module</a>. Topics provided by custom modules and themes are also translatable if they have been viewed at least once in a non-English language, which triggers putting their translatable text into the translation database.', [':locale_help' => (\Drupal::moduleHandler()->moduleExists('locale')) ? Url::fromRoute('help.page', ['name' => 'locale'])->toString() : '#']) . '</dd>';
       $output .= '</dl>';
diff -u b/core/modules/help_topics/src/HelpTopicDiscovery.php b/core/modules/help_topics/src/HelpTopicDiscovery.php
--- b/core/modules/help_topics/src/HelpTopicDiscovery.php
+++ b/core/modules/help_topics/src/HelpTopicDiscovery.php
@@ -10,7 +10,15 @@
 use Drupal\Core\StringTranslation\TranslatableMarkup;
 
 /**
- * Discovers help topic plugins from twig templates in help_topics directories.
+ * Discovers help topic plugins from Twig files in help_topics directories.
+ *
+ * @see \Drupal\help_topics\HelpTopicTwig
+ * @see \Drupal\help_topics\HelpTopicTwigLoader
+ *
+ * @internal
+ *   Help Topic is currently experimental and should only be leveraged by
+ *   experimental modules and development releases of contributed modules.
+ *   See https://www.drupal.org/core/experimental for more information.
  */
 class HelpTopicDiscovery implements DiscoveryInterface {
 
@@ -91,11 +99,12 @@
           // '.html.twig' is removed
           'id' => substr(basename($file), 0, -10),
           'provider' => $provider,
+          'class' => HelpTopicTwig::class,
           static::FILE_KEY => $file,
         ];
 
         // Get the rest of the plugin definition from meta tags contained in the
-        // help topic twig template.
+        // help topic Twig file.
         foreach (get_meta_tags($file) as $key => $value) {
           $key = substr($key, 11);
           switch ($key) {
@@ -112,6 +121,9 @@
               throw new DiscoveryException("The $file contains invalid meta tag with name='$key'");
           }
         }
+        if (!isset($data['label'])) {
+          throw new DiscoveryException("The $file contains does not contain the required meta tag with name='label'");
+        }
 
         $all[$provider][$data['id']] = $data;
         $file_cache->set($file, $data);
diff -u b/core/modules/help_topics/src/HelpTopicPluginInterface.php b/core/modules/help_topics/src/HelpTopicPluginInterface.php
--- b/core/modules/help_topics/src/HelpTopicPluginInterface.php
+++ b/core/modules/help_topics/src/HelpTopicPluginInterface.php
@@ -9,11 +9,7 @@
 /**
  * Defines an interface for help topic plugin classes.
  *
- * Help topics can be created by adding a help_topics folder to your module.
- * Each help topic has a {topic_id}.help_topic.yml file. The default
- * implementation relies on a corresponding Twig template.
- *
- * @see \Drupal\help_topics\HelpTopicTwig
+ * @see \Drupal\help_topics\HelpTopicPluginManager
  *
  * @internal
  *   Help Topic is currently experimental and should only be leveraged by
diff -u b/core/modules/help_topics/src/HelpTopicPluginManager.php b/core/modules/help_topics/src/HelpTopicPluginManager.php
--- b/core/modules/help_topics/src/HelpTopicPluginManager.php
+++ b/core/modules/help_topics/src/HelpTopicPluginManager.php
@@ -10,11 +10,30 @@
 /**
  * Provides the default help_topic manager.
  *
- * Modules and themes can provide help topics in YAML files called
- * name_of_topic.help_topic.yml inside the module or theme sub-directory
+ * Modules and themes can provide help topics in .html.twig files called
+ * name-of-topic.help_topic.html.twig inside the module or theme sub-directory
  * help_topics.
  *
+ * The Twig file must contain a meta tag named 'help_topic:label'. It can also
+ * contain meta tags named 'help_topic:top_level' and 'help_topic:related'. For
+ * example:
+ * @code
+ * <!–– The translated label used in help listings. -->
+ * <meta name="help_topic:label" content="Configuring error responses, including 403/404 pages"/>
+ *
+ * <!–– Related help topics in a comma separated name-of-topic list. -->
+ * <meta name="help_topic:related" content="config-basic,maintenance"/>
+ *
+ * <!–– If present then the help topic will appear on admin/help. -->
+ * <meta name="help_topic:top_level"/>
+ * @endcode
+ *
+ * @see \Drupal\help_topics\HelpTopicDiscovery
  * @see \Drupal\help_topics\HelpTopicTwig
+ * @see \Drupal\help_topics\HelpTopicTwigLoader
+ * @see \Drupal\help_topics\HelpTopicPluginInterface
+ * @see \Drupal\help_topics\HelpTopicPluginBase
+ * @see hook_help_topics_info_alter()
  *
  * @internal
  *   Help Topic is currently experimental and should only be leveraged by
@@ -29,7 +48,7 @@
    * @var array
    */
   protected $defaults = [
-    // The plugin ID. Set by the plugin system based on the top-level YAML key.
+    // The plugin ID.
     'id' => '',
     // The title of the help topic plugin.
     'label' => '',
@@ -37,7 +56,8 @@
     'top_level' => '',
     // List of related topic machine names.
     'related' => [],
-    'class' => HelpTopicTwig::class,
+    // The class used to instantiate the plugin.
+    'class' => '',
     'cache_tag' => '',
   ];
 
@@ -59,6 +79,8 @@
    *   Cache backend instance to use.
    */
   public function __construct(ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler, CacheBackendInterface $cache_backend) {
+    // Note that the parent construct is not called because this not use
+    // annotated class discovery.
     $this->moduleHandler = $module_handler;
     $this->themeHandler = $theme_handler;
     $this->alterInfo('help_topics_info');
@@ -91,7 +113,7 @@
   }
 
   /**
-   * Checks to see if plugin is provided by an uninstalled module or theme.
+   * {@inheritdoc}
    */
   public function alterDefinitions(&$definitions) {
     parent::alterDefinitions($definitions);
@@ -105,7 +127,8 @@
           unset($definitions[$plugin_id]['related'][$key]);
           continue;
         }
-        // Ensure that the other plugin is related to this ID.
+        // Ensures that related topics are bi-directional. That is, ensures the
+        // other plugin is related to this one.
         if (isset($definitions[$related_id]) && !in_array($plugin_id, $definitions[$related_id]['related'], TRUE)) {
           $definitions[$related_id]['related'][] = $plugin_id;
         }
diff -u b/core/modules/help_topics/src/HelpTopicTwig.php b/core/modules/help_topics/src/HelpTopicTwig.php
--- b/core/modules/help_topics/src/HelpTopicTwig.php
+++ b/core/modules/help_topics/src/HelpTopicTwig.php
@@ -6,15 +6,10 @@
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
- * Represents a help topic plugin whose definition comes from a YAML file.
+ * Represents a help topic plugin whose definition comes from a Twig file.
  *
- * The YAML files are stored in subdirectory help_topics, and must be named
- * id.help_topic.yaml, where id is the plugin ID. Each YAML file has a
- * corresponding Twig template inside help_topics/templates. The Twig file
- * should be named help-topic-{topic-id}.html.twig, where {topic-id} is the
- * topic ID used in the YAML file, with the underscores swapped for hyphens.
- * For example: help_topics/basic_pages.help_topic.yml would have a
- * corresponding help_topics/templates/help-topic-basic-pages.html.twig.
+ * @see \Drupal\help_topics\HelpTopicDiscovery
+ * @see \Drupal\help_topics\HelpTopicTwigLoader
  *
  * @internal
  *   Help Topic is currently experimental and should only be leveraged by
@@ -41,6 +36,8 @@
    *   The plugin implementation definition.
    * @param \Drupal\help_topics\HelpTopicPluginManagerInterface $plugin_manager
    *   The help topic plugin manager.
+   * @param \Drupal\Core\Template\TwigEnvironment $twig
+   *   The Twig environment.
    */
   public function __construct(array $configuration, $plugin_id, $plugin_definition, HelpTopicPluginManagerInterface $plugin_manager, TwigEnvironment $twig) {
     parent::__construct($configuration, $plugin_id, $plugin_definition, $plugin_manager);
diff -u b/core/modules/help_topics/src/HelpTopicTwigLoader.php b/core/modules/help_topics/src/HelpTopicTwigLoader.php
--- b/core/modules/help_topics/src/HelpTopicTwigLoader.php
+++ b/core/modules/help_topics/src/HelpTopicTwigLoader.php
@@ -6,12 +6,14 @@
 use Drupal\Core\Extension\ThemeHandlerInterface;
 
 /**
- * Loads help topic templates from the filesystem.
+ * Loads help topic Twig files from the filesystem.
  *
  * This loader adds module and theme help topic paths to a help_topics namespace
- * to the Twig filesystem loader so that help_topics can be referenced, like
+ * to the Twig filesystem loader so that help_topics can be referenced, using
+ * '@help-topic/pluginId.html.twig'.
  *
- * @help-topic/config-basic.html.twig
+ * @see \Drupal\help_topics\HelpTopicDiscovery
+ * @see \Drupal\help_topics\HelpTopicTwig
  *
  * @internal
  *   Help Topic is currently experimental and should only be leveraged by
@@ -37,23 +39,23 @@
    */
   public function __construct($root_path, ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler) {
     parent::__construct([], $root_path);
-    // Add help_topics namespaced paths for modules and themes.
-    foreach ($module_handler->getModuleList() as $name => $extension) {
-      $this->addPath($extension->getPath() . '/help_topics');
-    }
-    foreach ($theme_handler->listInfo() as $name => $extension) {
-      $this->addPath($extension->getPath() . '/help_topics');
-    }
-
+    // Add help_topics directories for modules and themes in the 'help_topic'
+    // namespace.
+    array_map([$this, 'addExtension'], $module_handler->getModuleDirectories());
+    array_map([$this, 'addExtension'], $theme_handler->getThemeDirectories());
   }
 
   /**
-   * {@inheritdoc}
+   * Adds an extensions help_topics directory to the Twig loader.
+   *
+   * @param $path
+   *   The path to the extension.
    */
-  public function addPath($path, $namespace = self::MAIN_NAMESPACE) {
+  protected function addExtension($path) {
+    $path .= DIRECTORY_SEPARATOR . 'help_topics';
     if (is_dir($path)) {
       $this->cache = $this->errorCache = [];
-      $this->paths[$namespace][] = rtrim($path, '/\\');
+      $this->paths[self::MAIN_NAMESPACE][] = rtrim($path, '/\\');
     }
   }
 
diff -u b/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php b/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php
--- b/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php
+++ b/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php
@@ -170,7 +170,7 @@
     $this->drupalGet('admin/help/topic/help-test-theme');
     $session->pageTextContains('This is a theme provided topic.');
     $this->clickLink('Additional topic');
-    $this->assertLink('XYZ Help Test theme');
+    $session->linkExists('XYZ Help Test theme');
 
     // Verify that the non-top-level topics do not appear on the Help page.
     $this->drupalGet('admin/help');
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/help_topics/help_topics.api.php
@@ -0,0 +1,25 @@
+<?php
+
+/**
+ * @file
+ * Hooks provided by the Help Topics module.
+ */
+
+/**
+ * @addtogroup hooks
+ * @{
+ */
+
+/**
+ * Perform alterations on help topic definitions.
+ *
+ * @param array $info
+ *   Array of information exposed by help topic plugins.
+ */
+function hook_help_topics_info_alter(&$info) {
+  // @todo
+}
+
+/**
+ * @} End of "addtogroup hooks".
+ */