This was briefly leaked: anyone typing in an email into a yet empty column would get this hidden control type. Then this got fixed because the control is not ready. I asked Coda because I also spotted it in some other doc.
On a different note, it’s also interesting that this New Relic doc is exactly the same as the one I’ve been recently given by one of my clients to rearchitect — even some categories and their icons are the same! One of the first things I did interface-wise was getting rid of the long list of duplicated categories per role and location, and making it a user-specific single-page UI with these “quick filters” instead:
