* An associative array of all entity bundles, keyed by the entity
* type name, and then the bundle name, with the following keys:
* - label: The human-readable name of the bundle.
- * - uri_callback: The same as the 'uri_callback' key defined for the entity
- * type in the EntityManager, but for the bundle only. When determining
- * the URI of an entity, if a 'uri_callback' is defined for both the
- * entity type and the bundle, the one for the bundle is used.
+ * - uri_callback: (optional) The same as the 'uri_callback' key defined for
+ * the entity type in the EntityManager, but for the bundle only. When
+ * determining the URI of an entity, if a 'uri_callback' is defined for both
+ * the entity type and the bundle, the one for the bundle is used.
* - translatable: (optional) A boolean value specifying whether this bundle
* has translation support enabled. Defaults to FALSE.
*