[Beta 9.1] Unused $extraHtml variable in \IPS\Helpers\Menu\Link

As mentioned in the title, the class \IPS\Helpers\Menu\Link defines the $extraHtml variable but it's not used anywhere:

public string $extraHtml = '';

I thought I could use it to add an image to my link, but the variable itself is only defined and not called/used anywhere (PHP or template).