phpbb extension

footer.php

<?php
namespace bee\wpfooter;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use phpbb\template\template;

class footer implements EventSubscriberInterface
{
  protected $template;
  protected $root_path;

  public function __construct(
    \phpbb\template\template $template,
    $phpbb_root_path
  ) {
    $this->template = $template;
    $this->root_path = $phpbb_root_path;
  }

  /**
   * Assign functions defined in this class to event listeners in the core
   *
   * @return array
   **/
  static public function getSubscribedEvents()
  {
    return array(
      'overall_footer_iframe' => 'load_footer',
    );
  }

  /**
   * Load the site-wide footer
   *
   * @param \phpbb\event\data $event The event object
   **/
  public function load_footer($event)
  {
    $this->template->assign_vars(array(
      'footer_frame' => '<h1>jfnf</h1>',
    ));
  }
}

overall_footer.html

<!-- EVENT overall_footer_iframe -->
{$footer_frame}

services.yml

services:
    bee.wpfooter.listener:
        class: bee\wpfooter\footer
        arguments:
            - @template
            - %core.root_path%
        tags:
            - { name: event.listener }