In a spec update timed perfectly for Pi day, Google has introduced some interesting new guidelines for developers and designers including - love it or hate it - bottom bar navigation.

Besides bottom bars (which we'll talk about in just a moment), Google has new guidance on split screen design (for Android only right now), advice for displaying passwords in input fields, and expanded guidance on accessibility including color, contrast, sound, motion, and hierarchy.

Back to bottom bars, though. We've seen this navigation pattern emerging in Photos and Google+ over the past months, and we've been questioning whether it might become A Thing on Android just as long. Interestingly, the material spec guidance doesn't fully line up with what we've experienced in Photos and G+, but it would make sense to consider those two apps sort of testing grounds for the pattern.

Google says the bar should hold between three and five items representing destinations that require access from anywhere in the app, and even recommends regular tabs as an "alternative" for one or two destinations. Google warns though that mixing these two patterns may cause confusion in navigating an interface, but does recommend using a drawer for destinations that don't fit on the bottom bar.

The spec goes on to explain how to color and label bottom bar icons and how they should behave, for example tapping an icon must go directly to a destination (not a menu or popup) or refresh the currently active view.

There's even a nice animation showing how views should transition when controlled by the bottom bar:

It would be fair to read Google's early guidance on bottom bars as somewhat cautious. After all, this is an emerging pattern (or re-emerging, depending on who you ask) on Android, so the nuances of how the bar should be used aren't set in stone. Plus, these are the material guidelines, not a hard rule book. As always, developers and designers should weigh what makes sense in their own context for their own product, using the guidelines as general best practices for any patterns they find to be necessary.

Check out the full update and all the bottom bar goodness at the link below.