45 files declare their use of Unicode

BookManager.php in core/modules/book/src/BookManager.php
bootstrap.inc in core/includes/bootstrap.inc
Functions that need to be loaded on every Drupal request.
CommentAdminOverview.php in core/modules/comment/src/Form/CommentAdminOverview.php
CommentAdminTest.php in core/modules/comment/tests/src/Functional/Views/CommentAdminTest.php
CommentForm.php in core/modules/comment/src/CommentForm.php
CommentPermalinkFormatter.php in core/modules/comment/src/Plugin/Field/FieldFormatter/CommentPermalinkFormatter.php
CommentTestTrait.php in core/modules/comment/src/Tests/CommentTestTrait.php
Connection.php in core/lib/Drupal/Core/Database/Driver/mysql/Connection.php
CssOptimizer.php in core/lib/Drupal/Core/Asset/CssOptimizer.php
DateTestBase.php in core/modules/datetime/tests/src/Functional/DateTestBase.php
DbLogController.php in core/modules/dblog/src/Controller/DbLogController.php
DbLogTest.php in core/modules/dblog/tests/src/Functional/DbLogTest.php
DefaultProcessor.php in core/modules/aggregator/src/Plugin/aggregator/processor/DefaultProcessor.php
DependencyTest.php in core/modules/system/tests/src/Functional/Module/DependencyTest.php
file.module in core/modules/file/file.module
Defines a "managed_file" Form API field and a "file" field for Field module.
FileSystem.php in core/lib/Drupal/Core/File/FileSystem.php
filter.module in core/modules/filter/filter.module
Framework for handling the filtering of content.
HandlerBase.php in core/modules/views/src/Plugin/views/HandlerBase.php
ImageStyleEditForm.php in core/modules/image/src/Form/ImageStyleEditForm.php
InOperator.php in core/modules/views/src/Plugin/views/filter/InOperator.php
install.inc in core/includes/install.inc
API functions for installing modules and themes.
JsOptimizer.php in core/lib/Drupal/Core/Asset/JsOptimizer.php
LinkFieldTest.php in core/modules/link/tests/src/Functional/LinkFieldTest.php
LinkFormatter.php in core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
LinkSeparateFormatter.php in core/modules/link/src/Plugin/Field/FieldFormatter/LinkSeparateFormatter.php
MailTest.php in core/modules/system/tests/src/Kernel/Mail/MailTest.php
MenuLink.php in core/modules/menu_link_content/src/Plugin/migrate/source/MenuLink.php
MenuLinkTest.php in core/modules/menu_link_content/tests/src/Kernel/Plugin/migrate/source/MenuLinkTest.php
MenuParentFormSelector.php in core/lib/Drupal/Core/Menu/MenuParentFormSelector.php
OverviewTerms.php in core/modules/taxonomy/src/Form/OverviewTerms.php
PathAliasListBuilder.php in core/modules/path/src/PathAliasListBuilder.php
PathBasedBreadcrumbBuilder.php in core/modules/system/src/PathBasedBreadcrumbBuilder.php
PathProcessorLanguage.php in core/modules/language/src/HttpKernel/PathProcessorLanguage.php
PhpMail.php in core/lib/Drupal/Core/Mail/Plugin/Mail/PhpMail.php
Schema.php in core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
SchemaTest.php in core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php
search.module in core/modules/search/search.module
Enables site-wide keyword searching.
SearchPageTextTest.php in core/modules/search/tests/src/Functional/SearchPageTextTest.php
SearchPluginBase.php in core/modules/search/src/Plugin/SearchPluginBase.php
system.install in core/modules/system/system.install
Install, update and uninstall functions for the system module.
text.module in core/modules/text/text.module
Defines simple text field types.
unicode.inc in core/includes/unicode.inc
Provides Unicode-related conversions and operations.
UnicodeTest.php in core/tests/Drupal/Tests/Component/Utility/UnicodeTest.php
user.module in core/modules/user/user.module
Enables the user registration and login system.
VocabularyPermissionsTest.php in core/modules/taxonomy/tests/src/Functional/VocabularyPermissionsTest.php

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