Issue #2822611 by Mile23, Wim Leers, alexpott, Berdir, catch, dawehner, xjm,...

Issue #2822611 by Mile23, Wim Leers, alexpott, Berdir, catch, dawehner, xjm, tstoeckler, borisson_: Document why UserInterface + FileInterface + MenuLinkContentInterface + … extend \Drupal\Core\Entity\ContentEntityInterface

core/lib/Drupal/Core/Entity/ContentEntityInterface.php

@@ -5,16 +5,19 @@
 /**
  * Defines a common interface for all content entity objects.
  *
- * Content entities use fields for all their entity properties and are
- * translatable and revisionable, while translations and revisions can be
- * enabled per entity type. It's best practice to always implement
- * ContentEntityInterface for content-like entities that should be stored in
- * some database, and enable/disable revisions and translations as desired.
+ * Content entities use fields for all their entity properties and can be
+ * translatable and revisionable. Translations and revisions can be
+ * enabled per entity type through annotation and using entity type hooks.
+ *
+ * It's best practice to always implement ContentEntityInterface for
+ * content-like entities that should be stored in some database, and
+ * enable/disable revisions and translations as desired.
  *
  * When implementing this interface which extends Traversable, make sure to list
  * IteratorAggregate or Iterator before this interface in the implements clause.
  *
  * @see \Drupal\Core\Entity\ContentEntityBase
+ * @see \Drupal\Core\Entity\EntityTypeInterface
  *
  * @ingroup entity_api
  */

core/lib/Drupal/Core/Entity/EntityTypeInterface.php

@@ -7,10 +7,19 @@
 /**
  * Provides an interface for an entity type and its metadata.
  *
- * Additional information can be provided by modules: hook_entity_type_build() can be
- * implemented to define new properties, while hook_entity_type_alter() can be
- * implemented to alter existing data and fill-in defaults. Module-specific
- * properties should be documented in the hook implementations defining them.
+ * Entity type classes can provide docblock annotations. The entity type manager
+ * will use these annotations to populate the entity type object with
+ * properties.
+ *
+ * Additional properties can be defined by module implementations of
+ * hook_entity_type_build(). Existing data can be altered in implementations of
+ * hook_entity_type_alter(), which can also be used to fill in defaults.
+ * Module-specific properties should be documented in the hook implementations
+ * defining them.
+ *
+ * @see \Drupal\Core\Entity\EntityTypeManagerInterface
+ * @see hook_entity_type_build()
+ * @see hook_entity_type_alter()
  */
 interface EntityTypeInterface extends PluginDefinitionInterface {
 

core/lib/Drupal/Core/Entity/RevisionableInterface.php

@@ -4,6 +4,21 @@
 
 /**
  * Provides methods for an entity to support revisions.
+ *
+ * Classes implementing this interface do not necessarily support revisions.
+ *
+ * To detect whether an entity type supports revisions, call
+ * EntityTypeInterface::isRevisionable().
+ *
+ * Many entity interfaces are composed of numerous other interfaces such as this
+ * one, which allow implementations to pick and choose which features to.
+ * support through stub implementations of various interface methods. This means
+ * that even if an entity class implements RevisionableInterface, it might only
+ * have a stub implementation and not a functional one.
+ *
+ * @see \Drupal\Core\Entity\EntityTypeInterface::isRevisionable()
+ * @see https://www.drupal.org/docs/8/api/entity-api/structure-of-an-entity-annotation
+ * @see https://www.drupal.org/docs/8/api/entity-api/making-an-entity-revisionable
  */
 interface RevisionableInterface {
 

core/lib/Drupal/Core/TypedData/TranslatableInterface.php

@@ -4,6 +4,21 @@
 
 /**
  * Interface for translatable data.
+ *
+ * Classes implementing this interface do not necessarily support translations.
+ *
+ * To detect whether an entity type supports translation, call
+ * EntityTypeInterface::isTranslatable().
+ *
+ * Many entity interfaces are composed of numerous other interfaces such as this
+ * one, which allow implementations to pick and choose which features to support
+ * through stub implementations of various interface methods. This means that
+ * even if an entity class implements TranslatableInterface, it might only have
+ * a stub implementation and not a functional one.
+ *
+ * @see \Drupal\Core\Entity\EntityTypeInterface::isTranslatable()
+ * @see https://www.drupal.org/docs/8/api/entity-api/structure-of-an-entity-annotation
+ * @see https://www.drupal.org/docs/8/api/entity-api/entity-translation-api
  */
 interface TranslatableInterface {