boot.php

<?php

use FriendsOfRedaxo\BlockPeek\TemplateListHider;

/** @var rex_addon_interface $addon */
$addon = $this;

if ($addon->getConfig('inactive') !== '|1|') {
    if (rex::isBackend() && rex::getUser()) {
        rex_view::addJsFile($this->getAssetsUrl('BlockPeek.js'));
        rex_view::addCssFile($this->getAssetsUrl('BlockPeek.css'));
        rex_extension::register('PACKAGES_INCLUDED', function () {
            rex_extension::register('SLICE_BE_PREVIEW', \FriendsOfRedaxo\BlockPeek\Extension::register(...), rex_extension::LATE);
        });
    }
}

// Hide the internal block_peek template row from the backend templates list page.
if (rex::isBackend()) {
    rex_extension::register('OUTPUT_FILTER', [TemplateListHider::class, 'register'], rex_extension::LATE);
}