* - During many operations, static methods are called on the entity class,
* which implements \Drupal\Entity\EntityInterface.
*
+ * @section entities_revisions_translations Entities, revisions and translations
+ * A content entity can have multiple stored variants: based on its definition,
+ * it can be revisionable, translatable, or both.
+ *
+ * A revisionable entity can keep track of the changes that affect its data. In
+ * fact all previous revisions of the entity can be stored and made available as
+ * "historical" information. The "default" revision is the canonical variant of
+ * the entity, the one that is loaded when no specific revision is requested.
+ * Only changes to the default revision may be performed without triggering the
+ * creation of a new revision, in any other case revision data is not supposed
+ * to change. Aside from historical revisions, there can be "pending" revisions,
+ * that contain changes that did not make their way into the default revision.
+ * Typically these revisions contain data that is waiting for some form of
+ * approval, before being accepted as canonical.
+ * @see \Drupal\Core\Entity\RevisionableInterface
+ * @see \Drupal\Core\Entity\RevisionableStorageInterface
+ *
+ * A translatable entity can contain multiple translations of the same content.
+ * Content entity data is stored via fields, and each field can have one version
+ * for each enabled language. Some fields may be defined as untranslatable,
+ * which means that their values are shared among all translations. The
+ * "default" translation is the canonical variant of the entity, the one whose
+ * content will be accessible in the entity field data. Other translations
+ * can be instantiated from the default one. Every translation has an "active
+ * language" that is used to determine which field translation values should be
+ * handled. Typically the default translation's active language is the language
+ * of the content that was originally entered and served as source for the other
+ * translations.
+ * @see \Drupal\Core\Entity\TranslatableInterface
+ * @see \Drupal\Core\Entity\TranslatableStorageInterface
+ *
+ * An entity that is both revisionable and translatable has all the features
+ * described above: every revision can contain one or more translations. The
+ * canonical variant of the entity is the default translation of the default
+ * revision. Any revision will be initially loaded as the default translation,
+ * the other revision translations can be instantiated from this one. If a
+ * translation has changes in a certain revision, the translation is considered
+ * "affected" by that revision, and will be flagged as such via the
+ * "revision_translation_affected" field. With the built-in UI, every time a new
+ * revision is saved, the changes for the edited translations will be stored,
+ * while all field values for the other translations will be copied as-is.
+ * However, if multiple translations of the default revision are being
+ * subsequently modified without creating a new revision when saving, they will
+ * all be affected by the default revision. Additionally, all revision
+ * translations will be affected when saving a revision containing changes for
+ * untranslatable fields. On the other hand, pending revisions are not supposed
+ * to contain multiple affected translations, even when they are being
+ * manipulated via the API.
+ * @see \Drupal\Core\Entity\TranslatableRevisionableInterface
+ * @see \Drupal\Core\Entity\TranslatableRevisionableStorageInterface
+ *
* @section create Create operations
* To create an entity:
* @code
* Hooks invoked during the create operation:
* - hook_ENTITY_TYPE_create()
* - hook_entity_create()
+ * - When handling content entities, if a new translation is added to the entity
+ * object:
+ * - hook_ENTITY_TYPE_translation_create()
+ * - hook_entity_translation_create()
*
* See @ref save below for the save portion of the operation.
*
* @endcode
* This involves the same hooks and operations as regular entity loading.
*
- * @section entities_revisions_translations Entities, revisions and translations
+ * The "latest revision" of an entity is the most recently created one,
+ * regardless of it being default or pending. If the entity is translatable,
+ * revision translations are not taken into account either. In other words, any
+ * time a new revision is created, that becomes the latest revision for the
+ * entity overall, regardless of the affected translations. To load the latest
+ * revision of an entity:
+ * @code
+ * $revision_id = $storage->getLatestRevisionId($entity_id);
+ * $entity = $storage->loadRevision($revision_id);
+ * @endcode
+ * As usual, if the entity is translatable, this code instantiates into $entity
+ * the default translation of the revision, even if the latest revision contains
+ * only changes to a different translation:
+ * @code
+ * $is_default = $entity->isDefaultTranslation(); // returns TRUE
+ * @endcode
*
- * A translation is not a revision and a revision is not necessarily a
- * translation. Revisions and translations are the two axes on the "spreadsheet"
- * of an entity. If you use the built-in UI and have revisions enabled, then a
- * new translation change would create a new revision (with a copy of all data
- * for other languages in that revision). If an entity does not use revisions or
- * the entity is being modified via the API, then multiple translations can be
- * modified in a single revision. Conceptually, the revisions are columns on the
- * spreadsheet and translations are rows.
+ * The "latest translation-affected revision" is the most recently created one
+ * that affects the specified translation. For example, when a new revision
+ * introducing some changes to an English translation is saved, that becomes the
+ * new "latest revision". However, if an existing Italian translation was not
+ * affected by those changes, then the "latest translation-affected revision"
+ * for Italian remains what it was. To load the Italian translation at its
+ * latest translation-affected revision:
+ * @code
+ * $revision_id = $storage->getLatestTranslationAffectedRevisionId($entity_id, 'it');
+ * $it_translation = $storage->loadRevision($revision_id)->getTranslation('it');
+ * @endcode
*
* @section save Save operations
* To update an existing entity, you will need to load it, change properties,
* - Comment: hook_comment_publish() and hook_comment_unpublish() as
* appropriate.
*
+ * Note that all translations available for the entity are stored during a save
+ * operation. When saving a new revision, a copy of every translation is stored,
+ * regardless of it being affected by the revision.
+ *
* @section edit Editing operations
* When an entity's add/edit form is used to add or edit an entity, there
* are several hooks that are invoked:
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