Mark Zuckerberg has a 'yellow' version of Facebook on his phone with all kinds of special features

Mark Zuckerberg showed off an internal Facebook-only version of its iPhone app during a live video this week, as part of the introduction of Facebook's live broadcasting feature.

As previously noticed by The Verge, the app includes several features that you can't get on the normal iPhone app.

First, as he opens it, he mentions that this is the "yellow version of the Facebook app, which is our internal build." You can see it briefly on the screen here:

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Later, as he demonstrates one way to start broadcasting live video, he says "you can tap on the composer at the top," as he selects the "Whats on your mind?" button:

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And that rolls out a new kind of menu with a list of content types you can post.

Facebook confirmed to The Verge that this interface has rolled out to some people already, although it's not on my version of the Facebook app. 

Within that list, there are buttons for posting Music, Slideshows, and GIFs, suggesting some pretty cool new features could be coming to the mobile app soon.

Rumors have swirled that Facebook's been building a music service since at least last summer, and it's supported posting GIFs since May 2015 but there hasn't been any specific button for them. "Slideshow" would presumably let you post a bunch of related pictures in slideshow format, like another test noticed last summer, although it may also refer to the new type of Slideshow advertising format that Facebook introduced last year for emerging markets.

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Zuck cautioned that not all of the features in the video would show up in the live app, and Facebook tests different interfaces all the time. But it's still a tantalizing glimpse of how Facebook works and some of the things it's considering to increase user engagement.

Here's the full video to check out yourself. The demo starts around 7:00.