diff --git a/core/modules/entity_reference/src/Annotation/EntityReferenceSelection.php b/core/modules/entity_reference/src/Annotation/EntityReferenceSelection.php
index afc6036..dbf6a51 100644
--- a/core/modules/entity_reference/src/Annotation/EntityReferenceSelection.php
+++ b/core/modules/entity_reference/src/Annotation/EntityReferenceSelection.php
@@ -10,7 +10,18 @@
 use Drupal\Component\Annotation\Plugin;
 
 /**
- * Defines a EntityReferenceSelection annotation object.
+ * Defines an EntityReferenceSelection plugin annotation object.
+ *
+ * Plugin Namespace: Plugin\entity_reference\selection
+ *
+ * For a working example, see
+ * \Drupal\comment\Plugin\entity_reference\selection\CommentSelection
+ *
+ * @see \Drupal\entity_reference\Plugin\Type\SelectionPluginManager
+ * @see \Drupal\entity_reference\Plugin\Type\Selection\SelectionInterface
+ * @see \Drupal\entity_reference\Plugin\entity_reference\selection\SelectionBase
+ * @see \Drupal\entity_reference\Plugin\Derivative\SelectionBase
+ * @see plugin_api
  *
  * @Annotation
  */
diff --git a/core/modules/entity_reference/src/Plugin/Derivative/SelectionBase.php b/core/modules/entity_reference/src/Plugin/Derivative/SelectionBase.php
index 79a8327..cb88855 100644
--- a/core/modules/entity_reference/src/Plugin/Derivative/SelectionBase.php
+++ b/core/modules/entity_reference/src/Plugin/Derivative/SelectionBase.php
@@ -10,7 +10,13 @@
 use Drupal\Component\Plugin\Derivative\DerivativeBase;
 
 /**
- * Base class for selection plugins provided by Entity Reference.
+ * Provides derivative plugins for Entity Reference Selection plugins.
+ *
+ * @see \Drupal\entity_reference\Plugin\entity_reference\selection\SelectionBase
+ * @see \Drupal\entity_reference\Plugin\Type\SelectionPluginManager
+ * @see \Drupal\entity_reference\Annotation\EntityReferenceSelection
+ * @see \Drupal\entity_reference\Plugin\Type\Selection\SelectionInterface
+ * @see plugin_api
  */
 class SelectionBase extends DerivativeBase {
   /**
diff --git a/core/modules/entity_reference/src/Plugin/Type/Selection/SelectionInterface.php b/core/modules/entity_reference/src/Plugin/Type/Selection/SelectionInterface.php
index 27e1f21..28fc2c5 100644
--- a/core/modules/entity_reference/src/Plugin/Type/Selection/SelectionInterface.php
+++ b/core/modules/entity_reference/src/Plugin/Type/Selection/SelectionInterface.php
@@ -11,12 +11,13 @@
 use Drupal\Core\Field\FieldDefinitionInterface;
 
 /**
- * Interface definition for Entity Reference selection plugins.
+ * Interface definition for Entity Reference Selection plugins.
  *
- * This interface details the methods that most plugin implementations will want
- * to override. See \Drupal\field\Plugin\Type\Selection\SelectionBaseInterface
- * for base wrapping methods that should most likely be inherited directly from
- * Drupal\entity_reference\Plugin\Type\Selection\SelectionBase.
+ * @see \Drupal\entity_reference\Plugin\entity_reference\selection\SelectionBase
+ * @see \Drupal\entity_reference\Plugin\Type\SelectionPluginManager
+ * @see \Drupal\entity_reference\Annotation\EntityReferenceSelection
+ * @see \Drupal\entity_reference\Plugin\Derivative\SelectionBase
+ * @see plugin_api
  */
 interface SelectionInterface {
 
diff --git a/core/modules/entity_reference/src/Plugin/Type/SelectionPluginManager.php b/core/modules/entity_reference/src/Plugin/Type/SelectionPluginManager.php
index aa44f1c..ce5ff83 100644
--- a/core/modules/entity_reference/src/Plugin/Type/SelectionPluginManager.php
+++ b/core/modules/entity_reference/src/Plugin/Type/SelectionPluginManager.php
@@ -18,7 +18,13 @@
 use Drupal\entity_reference\Plugin\Type\Selection\SelectionBroken;
 
 /**
- * Plugin type manager for the Entity Reference Selection plugin.
+ * Plugin type manager for Entity Reference Selection plugins.
+ *
+ * @see \Drupal\entity_reference\Annotation\EntityReferenceSelection
+ * @see \Drupal\entity_reference\Plugin\Type\Selection\SelectionInterface
+ * @see \Drupal\entity_reference\Plugin\entity_reference\selection\SelectionBase
+ * @see \Drupal\entity_reference\Plugin\Derivative\SelectionBase
+ * @see plugin_api
  */
 class SelectionPluginManager extends DefaultPluginManager {
 
diff --git a/core/modules/entity_reference/src/Plugin/entity_reference/selection/SelectionBase.php b/core/modules/entity_reference/src/Plugin/entity_reference/selection/SelectionBase.php
index ae4f5fc..58f84dc 100644
--- a/core/modules/entity_reference/src/Plugin/entity_reference/selection/SelectionBase.php
+++ b/core/modules/entity_reference/src/Plugin/entity_reference/selection/SelectionBase.php
@@ -15,7 +15,16 @@
 use Drupal\entity_reference\Plugin\Type\Selection\SelectionInterface;
 
 /**
- * Plugin implementation of the 'selection' entity_reference.
+ * Default plugin implementation of the Entity Reference Selection plugin.
+ *
+ * Also serves as a base class for specific types of Entity Reference
+ * Selection plugins.
+ *
+ * @see \Drupal\entity_reference\Plugin\Type\SelectionPluginManager
+ * @see \Drupal\entity_reference\Annotation\EntityReferenceSelection
+ * @see \Drupal\entity_reference\Plugin\Type\Selection\SelectionInterface
+ * @see \Drupal\entity_reference\Plugin\Derivative\SelectionBase
+ * @see plugin_api
  *
  * @EntityReferenceSelection(
  *   id = "default",