15 files declare their use of JsonSchema

Attribute.php in core/lib/Drupal/Core/Template/Attribute.php
BooleanData.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/BooleanData.php
DateTimeIso8601Normalizer.php in core/modules/serialization/src/Normalizer/DateTimeIso8601Normalizer.php
DateTimeNormalizer.php in core/modules/serialization/src/Normalizer/DateTimeNormalizer.php
DecimalData.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/DecimalData.php
DurationIso8601.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/DurationIso8601.php
Email.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/Email.php
FloatData.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/FloatData.php
IntegerData.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/IntegerData.php
JsonSchemaReflectionTrait.php in core/modules/serialization/src/Normalizer/JsonSchemaReflectionTrait.php
NullNormalizer.php in core/modules/serialization/src/Normalizer/NullNormalizer.php
StringData.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/StringData.php
TextProcessed.php in core/modules/text/src/TextProcessed.php
TimeSpan.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/TimeSpan.php
Uri.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/Uri.php

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