test_assign_block_vars_listener.php

<?php

use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class phpbb_ext_test_event_test_assign_block_vars_listener implements EventSubscriberInterface
{
	static public function getSubscribedEvents()
	{
		return array(
			'core.assign_block_vars' => 'cabv',
		);
	}

	public function cabv($event)
	{
		$event['vararray']['POSTER_WARNINGS'] = true;
	}
}

test_viewtopic_postrow_listener.php

<?php

use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class phpbb_ext_test_event_test_viewtopic_postrow_listener implements EventSubscriberInterface
{
	static public function getSubscribedEvents()
	{
		return array(
			'core.viewtopic_postrow' => 'cvp',
		);
	}

	public function cvp($event)
	{
		$event['postrow']['POSTER_WARNINGS'] = true;
	}
}