Windows Phone 8.1 may have only just reached the general public, but it's already in line for a surprisingly large update. Microsoft has posted developer documents (sign-in required) for Windows Phone 8.1 GDR1, a tweak that fills in a few key hardware and software gaps. Aside from previously revealed folder support, the upgrade will allow for smart cases akin to HTC's Dot View or LG's QuickCircle. Phone makers will get to run special apps when the cover is closed, and specify what happens when it's open. This seemingly simple addition could be important, since The Verge claims that HTC is preparing a Windows Phone version of the new One -- such a device would need smart cover features to perform the same tricks as its Android counterpart.The revision should also enable more of the tablet-sized phones that are all the rage in some corners of the globe. It'll support a 1,280 x 768 resolution on screens as large as 7 inches, and there's a new 1,280 x 800 option useful for larger devices that use software navigation buttons. Other upgrades are smaller, but should be important in the long run -- the update should bring high-quality voice over LTE, higher-quality Bluetooth music (through aptX) and manufacturer-defined custom lock screens. There's no confirmed schedule for when GDR1 would arrive, but Microsoft is clearly getting close. It won't be surprising if the next big wave of Windows Phones ships with the new features built in.