22 files declare their use of DateFormat

CommentOrphanTest.php in core/modules/comment/tests/src/Kernel/CommentOrphanTest.php
CommentTokensHooks.php in core/modules/comment/src/Hook/CommentTokensHooks.php
DateFormatAccessControlHandlerTest.php in core/modules/system/tests/src/Kernel/DateFormatAccessControlHandlerTest.php
DateFormatResourceTestBase.php in core/tests/Drupal/FunctionalTests/Rest/DateFormatResourceTestBase.php
DateFormatTest.php in core/modules/jsonapi/tests/src/Functional/DateFormatTest.php
DateFormatTest.php in core/modules/system/tests/src/FunctionalJavascript/System/DateFormatTest.php
DateFormatValidationTest.php in core/tests/Drupal/KernelTests/Core/Entity/DateFormatValidationTest.php
DateRangeFieldTest.php in core/modules/datetime_range/tests/src/Functional/DateRangeFieldTest.php
Datetime.php in core/lib/Drupal/Core/Datetime/Element/Datetime.php
DateTimeFieldTest.php in core/modules/datetime/tests/src/Functional/DateTimeFieldTest.php
DateTimeTest.php in core/modules/system/tests/src/Functional/System/DateTimeTest.php
MigrateDateFormatTest.php in core/modules/system/tests/src/Kernel/Migrate/d6/MigrateDateFormatTest.php
NodeTokensHooks.php in core/modules/node/src/Hook/NodeTokensHooks.php
RollbackTest.php in core/tests/Drupal/FunctionalTests/Core/Recipe/RollbackTest.php
SearchSetLocaleTest.php in core/modules/search/tests/src/Kernel/SearchSetLocaleTest.php
SummaryLengthTest.php in core/modules/node/tests/src/Kernel/SummaryLengthTest.php
SystemTokensHooks.php in core/modules/system/src/Hook/SystemTokensHooks.php
TaxonomyTokensHooks.php in core/modules/taxonomy/src/Hook/TaxonomyTokensHooks.php
TimestampTest.php in core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
TimezoneTest.php in core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php
UserTimeZoneTest.php in core/modules/user/tests/src/Functional/UserTimeZoneTest.php
UserTokensHooks.php in core/modules/user/src/Hook/UserTokensHooks.php

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