TitleBlockPluginInterface

class \Drupal\Core\Block\Plugin\Block\PageTitleBlock implements \Drupal\Core\Block\TitleBlockPluginInterface extends \Drupal\Core\Block\BlockBase
class \Drupal\block_test\Plugin\Block\TestPageTitleMainContentAndMessagesBlock implements \Drupal\Core\Block\MainContentBlockPluginInterface, \Drupal\Core\Block\TitleBlockPluginInterface, \Drupal\Core\Block\MessagesBlockPluginInterface extends \Drupal\Core\Block\BlockBase

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