diff --git a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
index df6c3a7..28f7f97 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
@@ -12,7 +12,6 @@
 use Drupal\Core\Database\Database;
 use Drupal\Core\Entity\Query\QueryInterface;
 use Drupal\Core\Entity\Schema\ContentEntitySchemaHandler;
-use Drupal\Core\Entity\Schema\EntitySchemaProviderInterface;
 use Drupal\Core\Entity\Sql\DefaultTableMapping;
 use Drupal\Core\Entity\Sql\SqlEntityStorageInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
@@ -31,18 +30,24 @@
  *
  * This class can be used as-is by most simple entity types. Entity types
  * requiring special handling can extend the class.
+ *
+ * The class makes internally use of
+ * \Drupal\Core\Entity\Schema\ContentEntitySchemaHandler in order to
+ * automatically generate the database schema based on the defined base fields.
+ * Entity types can override ContentEntityDatabaseStorage::getSchema() to
+ * customize the generated schema; e.g., to add additional indexes.
  */
-class ContentEntityDatabaseStorage extends ContentEntityStorageBase implements SqlEntityStorageInterface, EntitySchemaProviderInterface {
+class ContentEntityDatabaseStorage extends ContentEntityStorageBase implements SqlEntityStorageInterface {
 
   /**
-   * The base field definitions for this entity type.
+   * The storage field definitions for this entity type.
    *
    * @var \Drupal\Core\Field\FieldStorageDefinitionInterface[]
    */
   protected $fieldStorageDefinitions;
 
   /**
-   * A mapping of schema fields that will be stored per entity table.
+   * The mapping of field columns to SQL tables.
    *
    * @var \Drupal\Core\Entity\Sql\TableMappingInterface
    */
@@ -58,7 +63,7 @@ class ContentEntityDatabaseStorage extends ContentEntityStorageBase implements S
   protected $revisionKey = FALSE;
 
   /**
-   * The entity langcode key
+   * The entity langcode key.
    *
    * @var string|bool
    */
@@ -665,7 +670,6 @@ public function save(EntityInterface $entity) {
       db_ignore_slave();
       return $return;
     }
-
     catch (\Exception $e) {
       $transaction->rollback();
       watchdog_exception($this->entityTypeId, $e);
@@ -719,7 +723,7 @@ protected function doSave($id, EntityInterface $entity) {
         ->execute();
       // Even if this is a new entity the ID key might have been set, in which
       // case we should not override the provided ID. An empty value for the
-      // ID is interpreted as NULL and thus overriden.
+      // ID is interpreted as NULL and thus overridden.
       if (empty($record->{$this->idKey})) {
         $record->{$this->idKey} = $insert_id;
       }
diff --git a/core/lib/Drupal/Core/Entity/Schema/ContentEntitySchemaHandler.php b/core/lib/Drupal/Core/Entity/Schema/ContentEntitySchemaHandler.php
index 22e7629..ff0031a 100644
--- a/core/lib/Drupal/Core/Entity/Schema/ContentEntitySchemaHandler.php
+++ b/core/lib/Drupal/Core/Entity/Schema/ContentEntitySchemaHandler.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Core\Entity\Schema\ContentEntitySchemaHandler.
@@ -11,7 +12,7 @@
 use Drupal\Core\Entity\EntityManagerInterface;
 
 /**
- * An entity schema builder that supports revisionable, translatable entities.
+ * Defines a schema handler that supports revisionable, translatable entities.
  */
 class ContentEntitySchemaHandler implements EntitySchemaHandlerInterface {
 
diff --git a/core/lib/Drupal/Core/Entity/Schema/EntitySchemaHandlerInterface.php b/core/lib/Drupal/Core/Entity/Schema/EntitySchemaHandlerInterface.php
index a151a29..a38b82c 100644
--- a/core/lib/Drupal/Core/Entity/Schema/EntitySchemaHandlerInterface.php
+++ b/core/lib/Drupal/Core/Entity/Schema/EntitySchemaHandlerInterface.php
@@ -1,12 +1,14 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Core\Entity\Schema\EntitySchemaHandlerInterface.
  */
+
 namespace Drupal\Core\Entity\Schema;
 
 /**
- * A common interface for building the storage schema for entities.
+ * Defines an interface for handling the storage schema of entities.
  */
 interface EntitySchemaHandlerInterface extends EntitySchemaProviderInterface {
 }
diff --git a/core/lib/Drupal/Core/Entity/Schema/EntitySchemaProviderInterface.php b/core/lib/Drupal/Core/Entity/Schema/EntitySchemaProviderInterface.php
index b606a31..c976782 100644
--- a/core/lib/Drupal/Core/Entity/Schema/EntitySchemaProviderInterface.php
+++ b/core/lib/Drupal/Core/Entity/Schema/EntitySchemaProviderInterface.php
@@ -1,12 +1,14 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Core\Entity\Schema\EntitySchemaProviderInterface.
  */
+
 namespace Drupal\Core\Entity\Schema;
 
 /**
- * A common interface to return the storage schema for entities.
+ * Defines a common interface to return the storage schema for entities.
  */
 interface EntitySchemaProviderInterface {
 
diff --git a/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php b/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php
index 92386e5..e872d57 100644
--- a/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php
+++ b/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Core\Entity\Sql\DefaultTableMapping.
@@ -7,7 +8,7 @@
 namespace Drupal\Core\Entity\Sql;
 
 /**
- * Manages a table mapping for an entity storage.
+ * Defines a default table mapping class.
  */
 class DefaultTableMapping implements TableMappingInterface {
 
diff --git a/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php b/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php
index c8ab0d7..8c4e3d8 100644
--- a/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php
+++ b/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Core\Entity\Sql\SqlEntityStorageInterface.
@@ -7,14 +8,15 @@
 namespace Drupal\Core\Entity\Sql;
 
 use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\Schema\EntitySchemaProviderInterface;
 
 /**
  * A common interface for SQL-based storage controllers.
  */
-interface SqlEntityStorageInterface extends EntityStorageInterface {
+interface SqlEntityStorageInterface extends EntityStorageInterface, EntitySchemaProviderInterface {
 
   /**
-   * Gets a table mapping for the entity's tables.
+   * Gets a table mapping for the entity's SQL tables.
    *
    * @return \Drupal\Core\Entity\Sql\TableMappingInterface
    *   A table mapping object for the entity's tables.
diff --git a/core/lib/Drupal/Core/Entity/Sql/TableMappingInterface.php b/core/lib/Drupal/Core/Entity/Sql/TableMappingInterface.php
index 422daa3..0acc343 100644
--- a/core/lib/Drupal/Core/Entity/Sql/TableMappingInterface.php
+++ b/core/lib/Drupal/Core/Entity/Sql/TableMappingInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Core\Entity\Sql\TableMappingInterface.
@@ -7,7 +8,7 @@
 namespace Drupal\Core\Entity\Sql;
 
 /**
- * Provides a common interface for table mapping implementations.
+ * Provides a common interface for mapping field columns to SQL tables.
  */
 interface TableMappingInterface {
 
@@ -56,7 +57,7 @@ public function getFieldNames($table_name);
   public function getColumnNames($field_name);
 
   /**
-   * Returns a list of database columns which store denormalized data.
+   * Returns a list of extra database columns, which store denormalized data.
    *
    * These database columns do not belong to any entity fields. Any normalized
    * data that is stored should be associated with an entity field.
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
index a5d37b8..a36c98c 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
@@ -115,8 +115,8 @@ public static function schema(FieldStorageDefinitionInterface $field_definition)
         'target_id' => array(
           'description' => 'The ID of the target entity.',
           'type' => 'varchar',
-          // If the target entities act as bundles for another entity type, their
-          // IDs should not exceed the maximum length for bundles.
+          // If the target entities act as bundles for another entity type,
+          // their IDs should not exceed the maximum length for bundles.
           'length' => $target_type_info->getBundleOf() ? EntityTypeInterface::BUNDLE_MAX_LENGTH : 255,
         ),
       );
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockStorage.php b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockStorage.php
index 32b9db0..b7b8711 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockStorage.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockStorage.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\custom_block\CustomBlockStorage.
diff --git a/core/modules/node/lib/Drupal/node/NodeStorage.php b/core/modules/node/lib/Drupal/node/NodeStorage.php
index 71831bf..8f87df5 100644
--- a/core/modules/node/lib/Drupal/node/NodeStorage.php
+++ b/core/modules/node/lib/Drupal/node/NodeStorage.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\node;
 
-use Drupal\Core\Database\Database;
 use Drupal\Core\Entity\ContentEntityDatabaseStorage;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Language\Language;
diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/WriteRecordTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/WriteRecordTest.php
index da88eda..fd6ac63 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/WriteRecordTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/WriteRecordTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\system\Tests\Common;
 
 use Drupal\simpletest\DrupalUnitTestBase;
-use Drupal\simpletest\WebTestBase;
 
 /**
  * Tests writing of data records with drupal_write_record().
diff --git a/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php b/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php
index f347b2a..b39fbcb 100644
--- a/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Tests\Core\Entity\Schema\ContentEntitySchemaHandlerTest.
diff --git a/core/tests/Drupal/Tests/Core/Entity/Sql/DefaultTableMappingTest.php b/core/tests/Drupal/Tests/Core/Entity/Sql/DefaultTableMappingTest.php
index 501315d..196ff77 100644
--- a/core/tests/Drupal/Tests/Core/Entity/Sql/DefaultTableMappingTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/Sql/DefaultTableMappingTest.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Contains \Drupal\Tests\Core\Entity\Sql\DefaultTableMappingTest.