Issue #3335796: Add hook help

entity_reference_display.module

@@ -8,6 +8,32 @@
 use Drupal\Component\Utility\Html;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\entity_reference_display\Plugin\Field\FieldFormatter\EntityReferenceRevisionsDisplayFormatter;
+use Drupal\Core\Routing\RouteMatchInterface;
+
+/**
+ * Implements hook_help().
+ */
+function entity_reference_display_help($route_name, RouteMatchInterface $route_match) {
+  switch ($route_name) {
+    // Main module help for the entity_reference_display module.
+    case 'help.page.entity_reference_display':
+      $output = '';
+      $output .= '<h3>' . t('About') . '</h3>';
+      $output .= '<p>' . t('This module defines a simple field type for display mode selection for entity
+      reference fields. This allows an editor to select how they would like the
+      references displayed. </p> <p> <strong>
+      "Display mode" field type: </strong> This field allows you to specify a display mode
+      for the rendering of entity reference fields. You can configure available
+      options to show only certain display modes. The user then selects one from these
+      and affects the way your entity reference field renders items.</p> <p>
+      <strong>"Selected display mode" field formatter:</strong> This formatter allows you to render
+      referenced entities with a selected display mode. The formatter is available
+      only for entity reference fields where the base entity contains at least one
+      display mode field. When there are more display fields available, you can choose
+      one.') . '</p>';
+      return $output;
+  }
+}
 
 /**
  * Implements hook_form_alter().