11 files declare their use of Index

BatchStorage.php in core/lib/Drupal/Core/Batch/BatchStorage.php
comment.install in core/modules/comment/comment.install
Install, update and uninstall functions for the Comment module.
database.api.php in core/lib/Drupal/Core/Database/database.api.php
Hooks related to the Database system and the Schema API.
dblog.install in core/modules/dblog/dblog.install
Install, update and uninstall functions for the dblog module.
DriverSpecificSchemaTestBase.php in core/tests/Drupal/KernelTests/Core/Database/DriverSpecificSchemaTestBase.php
file.install in core/modules/file/file.install
Install, update and uninstall functions for File module.
layout_builder.install in core/modules/layout_builder/layout_builder.install
Contains install and update functions for Layout Builder.
locale.install in core/modules/locale/locale.install
Install, update, and uninstall functions for the Locale module.
SchemaDefinitionConversionTest.php in core/tests/Drupal/Tests/Core/Database/SchemaDefinitionConversionTest.php
user.install in core/modules/user/user.install
Install, update and uninstall functions for the user module.
workspaces.install in core/modules/workspaces/workspaces.install
Contains install, update and uninstall functions for the Workspaces module.

Buggy or inaccurate documentation? Please file an issue. Need support? Need help programming? Connect with the Drupal community.