17 files declare their use of DescriptionTemplateTrait in Examples for Developers 3.x

AjaxExampleController.php in modules/ajax_example/src/Controller/AjaxExampleController.php

BlockExampleController.php in modules/block_example/src/Controller/BlockExampleController.php

FieldExampleController.php in modules/field_example/src/Controller/FieldExampleController.php

HooksExampleController.php in modules/hooks_example/src/Controller/HooksExampleController.php

JsExampleController.php in modules/js_example/src/Controller/JsExampleController.php

MenuExampleController.php in modules/menu_example/src/Controller/MenuExampleController.php

NodeTypeExampleController.php in modules/node_type_example/src/Controller/NodeTypeExampleController.php

Page.php in modules/form_api_example/src/Controller/Page.php

PageExampleController.php in modules/page_example/src/Controller/PageExampleController.php

PHPUnitExampleController.php in modules/phpunit_example/src/Controller/PHPUnitExampleController.php

RenderExampleController.php in modules/render_example/src/Controller/RenderExampleController.php

RestExampleHelpController.php in modules/rest_example/src/Controller/RestExampleHelpController.php

RobotListBuilder.php in modules/config_entity_example/src/Controller/RobotListBuilder.php

SampleExampleController.php in tests/modules/examples_description_test/src/Controller/SampleExampleController.php

TableDragExampleController.php in modules/tabledrag_example/src/Controller/TableDragExampleController.php

TestingExampleController.php in modules/testing_example/src/Controller/TestingExampleController.php

TourExampleController.php in modules/tour_example/src/Controller/TourExampleController.php