User blog comment:Robinben1037/Fortresses and Inventions/@comment-25370207-20140919102349/@comment-4842859-20140919194614

The gui command is new (like, I snuck it in with the hotfix just a week ago), so that's probably why you didn't know about it.

However, this is just for your information: If you're in the 101 fanclub and are looking to get a promo from making stuff like this, the guis need to be visible in at least one of the pictures or you won't be promoted. That's just to be able to verify that it happened in an actual gameserver and not in studio or a private version.