+ /**
+ * Indicates whether the entity data is internal.
+ *
+ * This can be used in a scenario when it is not desirable to expose data of
+ * this entity type to an external system.
+ *
+ * The implications of this method are left to the discretion of the caller.
+ * For example, a module providing an HTTP API may not expose entities of
+ * this type or a custom entity reference field settings form may deprioritize
+ * entities of this type in a select list.
+ *
+ * @return bool
+ * TRUE if the entity data is internal, FALSE otherwise.
+ *
+ * @see \Drupal\Core\TypedData\DataDefinitionInterface::isInternal()
+ */
+ public function isInternal();
+