How do I use DocC to mark a portion of my package as beta?

I've noticed that many of the new APIs introduced at WWDC are showing as "Beta" in their documentation. I'd like to do the same for one of my Swift packages (specifically because these APIs themselves make use of said Beta API). I can't seem to find information on the annotation I'm supposed to use in my documentation comments to generate the "Beta" display label.

Could someone explain how this works in DocC? Thanks!