[Concrete CMS] Change Ckeditor DTD settings

site.php

<?php
// application/config/site.php
// https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_dtd.html

$dtd = <<<END
CKEDITOR.dtd['a']['div'] = 1;
END;

return [
    'sites' => [
        'default' => [
            'editor' => [
                'ckeditor4' => [
                    'editor_function_options' => $dtd
                ],
            ],
        ],
    ],
];