Google's Play Store has been rolling out a new nested tab interface to a limited subset of users on a testing basis, and it seems that the feature is now going to be making its way to a wider demographic, as suggested by recent reports. The interface change puts nested tabs underneath the category listings for the Play Store. Each category has its own set of tabs that present different types of results. The design tweak actually violates Material Design guidelines in that it puts a set of tabbed content underneath a tab. The fact that such a change passed testing and is now starting to roll out to all users may mean that Google is changing the Material Design guidelines, but it's just as likely that it's simply making an exception in this singular case to make a more user-friendly Play Store.
Users will find that each category now contains subcategories presented in the form of the new nested tabs. The names of all tabs are fairly self-explanatory; the "For You" heading, for example, contains apps that Google's algorithms think you would like. The "Top Charts" heading shows off the top apps in a category according to a few different metrics. The general "Categories" listing contains all of the subcategories like Android Wear and Arcade games within a given category. The "Editors' Choice" heading shows you games and apps in a given category that Google Play's own curators think are the best. The "Early Access" tab shows you apps and games that aren't quite ready for primetime but are open for testing. Finally, the "Family" tab shows off apps that are kid-friendly, arranged within age categories and under a "Top Charts" heading.
This nested tab interface flies directly in the face of applicable Material Design guidelines, which recommend using a content hierarchy instead. Ideally, the higher-category headings, such as Home, Games, Movies, and such, would each have their own screen. From there, the tabs that are now nested would take the place of the main tabs. Google has not officially announced this change, so there has not been any commentary as to why its experimental aesthetic is ignoring applicable Material Design guidelines or whether those guidelines will be changed.