10 files declare their use of Parser

common.inc in drupal/core/includes/common.inc
Common functions that many Drupal modules will need to reference.
DumperTest.php in drupal/core/vendor/symfony/yaml/Symfony/Component/Yaml/Tests/DumperTest.php
FileStorage.php in drupal/core/lib/Drupal/Core/Config/FileStorage.php
Definition of Drupal\Core\Config\FileStorage.
ModuleHandler.php in drupal/core/lib/Drupal/Core/Extension/ModuleHandler.php
Contains Drupal\Core\Extension\ModuleHandler.
ParserTest.php in drupal/core/vendor/symfony/yaml/Symfony/Component/Yaml/Tests/ParserTest.php
RouteBuilder.php in drupal/core/lib/Drupal/Core/Routing/RouteBuilder.php
Definition of Drupal\Core\Routing\RouteBuilder.
YamlFileLoader.php in drupal/core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php
Contains \Drupal\Core\DependencyInjection\YamlFileLoader.
YamlFileLoader.php in drupal/core/vendor/symfony/routing/Symfony/Component/Routing/Loader/YamlFileLoader.php
YamlFileLoader.php in drupal/core/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
YamlFileLoader.php in drupal/core/vendor/symfony/validator/Symfony/Component/Validator/Mapping/Loader/YamlFileLoader.php