7 files declare their use of JsonApiSpec

EntityAccessChecker.php in core/modules/jsonapi/src/Access/EntityAccessChecker.php
EntityReferenceFieldNormalizer.php in core/modules/jsonapi/src/Normalizer/EntityReferenceFieldNormalizer.php
JsonApiDocumentTopLevelNormalizer.php in core/modules/jsonapi/src/Normalizer/JsonApiDocumentTopLevelNormalizer.php
JsonApiRequestValidator.php in core/modules/jsonapi/src/EventSubscriber/JsonApiRequestValidator.php
JsonApiSpecTest.php in core/modules/jsonapi/tests/src/Unit/JsonApiSpecTest.php
Relationship.php in core/modules/jsonapi/src/JsonApiResource/Relationship.php
ResourceObject.php in core/modules/jsonapi/src/JsonApiResource/ResourceObject.php

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