8 files declare their use of TopBarItem

PageActions.php in core/modules/navigation/src/Plugin/TopBarItem/PageActions.php
PageContext.php in core/modules/navigation/src/Plugin/TopBarItem/PageContext.php
TopBarItemHigh.php in core/modules/navigation/tests/navigation_test/src/Plugin/TopBarItem/TopBarItemHigh.php
TopBarItemInstantiation.php in core/modules/navigation/tests/navigation_test/src/Plugin/TopBarItem/TopBarItemInstantiation.php
TopBarItemLinkAttribute.php in core/modules/navigation/tests/navigation_test_top_bar/src/Plugin/TopBarItem/TopBarItemLinkAttribute.php
TopBarItemLow.php in core/modules/navigation/tests/navigation_test/src/Plugin/TopBarItem/TopBarItemLow.php
TopBarItemManager.php in core/modules/navigation/src/TopBarItemManager.php
TopBarItemZero.php in core/modules/navigation/tests/navigation_test/src/Plugin/TopBarItem/TopBarItemZero.php

Buggy or inaccurate documentation? Please file an issue. Need support? Need help programming? Connect with the Drupal community.