TinyMCE max length validation

In the case we have a custom field like this:

function custom_wysiwyg(String $name, 
    bool $isRequired,
    bool $hasQuicktags,
    int $rows, 
    int $max_length,
    String $tags_allowed,
    String $formats_allowed
) {
    return [
        'name'     => $name,
        'id'       => strtolower($name),
        'type'     => 'wysiwyg',
        'required' => $isRequired,
        'options' => [
            'textarea_rows' => $rows,
            'tinymce' => [
                'block_formats' => $formats_allowed,
                'toolbar1' => $tags_allowed,
            ],
            'quicktags' => $hasQuicktags,
        ],
    ];
}

The validation would work? I did not understand the part of it not working with the Visual tab.