Less than a day after Microsoft is said to have provided select developers with access to its Windows Phone 8.1 software development kit, leaks about many of the alleged features coming in WP 8.1 hit the Web.

Up until now, there had been relatively few specifics about the Windows Phone 8.1 (codenamed "Blue") that had escaped Redmond. Word of plans for a coming notification center and the Microsoft Siri competitor codenamed "Cortana" had leaked. But details around the changes at the programming-interface level had been more guesses than anything.

Now, however, there's evidence that Microsoft has made some actual advances toward increased commonality between its Windows Phone and WinRT programming interfaces .

A self-identified Windows Phone developer published screen shots and details about the new "Universal App" template that will allow developers to reuse more of their Windows Store and Windows Phone code when building apps using JavaScript and HTML. Increased code reuse across platforms is one of the promises that Microsoft has made to its developers for the past year-plus.

That developer (going by the name "wpthrowaway" on Reddit) published this alleged screen shot of the Microsoft Connect portal that mentions "Universal App":

"(A)pps now can share XAML between WinRT and WP8 (sometimes whole pages)," wpthrowaway said.

Microsoft isn't expected to provide a common app store for Windows Phone and Windows Store apps until 2015, according to what I've heard from my contacts. But greater code use is a key step toward enabling this.

The Verge published a number of other features that are believed to be part of Windows Phone 8.1 based on the latest leaks, as has WPCentral. Among these claimed features:

Integrated VPN support (Previously, Microsoft execs had said VPN support would be coming as part of a separate "Enterprise Pack.

Battery Power Sense feature

New podcast app

IE 11 browser update with WebGL support (plus ability to play YouTube videos on the page)

Facebook account integration removed from Contacts hub

PlayTo support

Single sign-on persists across apps

Updated camera layout

Microsoft officials, predictably, are not commenting as to whether any of these leaked features are real.

"We regularly involve our developer community in a variety of private programs. We have nothing to share broadly about our recent developer outreach," a spokesperson said via a statement.

Microsoft took a lot of heat for holding off on providing its phone developers with early access to the Windows Phone 8 software development kit. This year, it seems the Softies decided to take the risk, even though the possibility of leaks would -- and seemingly did -- rise exponentially.

Update: RomanL (@AngelWZR on Twitter) has posted information indicating that there will be a separate Facebook "Blue" app that may be built into the Windows Phone 8.1 OS.

From what looks like official developer documentation, shared by RomanL: "Users can no longer broadcast share to multiple networks. Users of Twitter, Facebook, Sina Weibo and LinkedIn must use apps for these social networks to compose, post, and update. Facebook Blue is built into Windows Phone (code-named "Blue").

Developers also will still be able to "create a Silverlight-based Windows Phone (code-named “Blue”) app using C# or Visual Basic, or ... upgrade an existing Windows Phone 8.0 app to Windows Phone (code-named “Blue”)," according to additional information RomanL shared. In this case, Silverlight 8.1 refers to a new app model (not a new version of Silverlight) that will allow developers to enable their older apps to take advantage of some of the new Windows Phone 8.1 features, I hear.

Update No. 2 (February 12): RomanL is at it again. Here's a screen capture of more information from the developer preview about the "Universal App" concept:

As I noted yesterday, there are still two stores at this point: Windows Phone Store and Windows Store and two separate AppX packages. But there's one shared template, as of Windows Phone 8.1.