BARCELONA, Spain—Until today, Microsoft hasn't said a whole lot about development on Windows 10. We know "universal apps" that can run substantially unaltered on phones, tablets, desktop PCs, and even the Xbox—and maybe one day, the HoloLens—are core to Microsoft's Windows 10 vision. We know that these universal apps will build on the ground work laid by Windows 8.1 and Windows Phone 8.1. But beyond that, the company has kept very quiet about the developer story.

The big message is still "Wait for the Build conference in April," but today at MWC the company started to open up about app development on Windows 10, announcing one new feature that might help with the troublesome app gap.

Windows 10 will let developers publish Web apps through the store. These will be true Web apps, run remotely from a developer's existing Web infrastructure without any modifications. Windows 10 will still support HTML and JavaScript development, and it will still support Cordova/PhoneGap style development where Web apps are packaged and deployed locally. This will be a third option.

On its own, that might not seem a big deal; it turns existing Web apps into Windows apps, but the apps themselves won't change. However, Windows 10 will give these apps special powers.

Normally, browser-based apps are constrained by the browser sandbox. They have no access to operating system APIs, and they're given constrained access to, for example, persistent storage, cameras, and microphones. When a Web app is published for Windows 10, however, these constraints will be relaxed. The Web apps will be able to check if they're running as a special blessed app, and if so, they'll be able to do some of the things that normal apps can do (for example, generate Windows notifications or show full-screen video without prompting) that regular Web apps normally can't.

Microsoft hopes that this will bridge the gap for a lot of the companies out there who have a Web app, but for whom that Web app isn't their business. Banks are a typical example of this; most of them these days have capable online presences (often in addition to "real" apps on iOS and Android) that they'll always have to maintain and update.

Windows 10 will allow those banks to first do simple app things, like have a presence in the store, have a pinnable tile to launch the site, and so on. But Microsoft will now further allow those sites to be incrementally extended—such as letting them launch the camera app to scan a paper check—without requiring an entire Windows app to be developed.

This should also appeal to enterprises, as they increasingly use the Web to deliver in-house line-of-business software.

Appifying Web apps isn't going to solve every Windows app gap problem, and it's likely to do little to aid those gaps where the app itself is in some sense the business, such as Snapchat. In those situations, there's no Web app to fall back on. But as a way of helping Microsoft fill some important gaps while placing very low demands on developers, this approach could have some merit. We'll no doubt learn more about what can be done, and what the limitations are, at Build.