ixm_blocks-1.0.x-dev/modules/ixm_blocks_accordion/ixm_blocks_accordion.module

<?php

/**
 * @file
 * IXM Blocks Accordion submodule.
 */

/**
 * Implements hook_theme().
 */
function ixm_blocks_accordion_theme($existing, $type, $theme, $path) {
  return [
    'block__ixm_blocks_accordion' => [
      'base hook' => 'block',
      'template' => 'block--ixm-blocks-accordion',
    ],
  ];
}