Microsoft's faster release schedule for its Windows 10 Technical Preview kicked into high gear yesterday with the release of another build a mere 12 days after 10041. This time, with build 10049, Microsoft has added one of Windows 10's major new features: its next-generation Web browser.

With the new browser (code-name Project Spartan), Microsoft finally breaks from the need to support even the oldest of Web pages and Web technologies. Instead of incorporating Internet Explorer's Trident HTML and CSS rendering engine, Project Spartan is built around a new engine that is based on Trident's HTML5 features (and has been available in previous Windows 10 builds as Internet Explorer's Edge rendering option). Unlike Trident, the new browser engine is designed to be updated, which allows Microsoft to keep its new browser current in a way that was impossible with IE.

Windows 10 browser HTML5test.com compatibility score Apple Safari 8 396 Google Chrome 39 501 Microsoft Internet Explorer 11 348 Microsoft Project Spartan beta 375 Mozilla Firefox 35 449 Opera 26 497

There's a lot in Microsoft's new browser and, at least in this build, a lot that's been left out. You won't find support for device-to-device synchronization of tabs and browsing history or for the promised new extension model. Other features still to come include a download view, browsing history, a roaming reading list (synced across Windows 10 devices), and offline reading. You won't get access to all of Internet Explorer's plug-ins, either. Project Spartan will provide a level of plug-in support similar to Windows 8's Metro IE browser.

Microsoft is promising an offline reading experience that works across all your Windows 10 devices. While parts of it are still missing, a refreshed Reading View gives you a clear look at Web pages, which is ideal for reading on tablets and phones.

Project Spartan's user interface is reminiscent of other modern browsers while still remaining familiar to Internet Explorer users. There's direct access to Cortana from inside the browser (as demonstrated at Microsoft's January Windows 10 event in Redmond). Cortana can be activated from the browser's search bar. Building a search-based agent into a browser makes a lot of sense, especially when it's able to use the context of your searches and browser history to make inferences about what information you need -- initially giving you weather and stock information.

Microsoft has integrated Cortana with Project Spartan's search tools. While it's not yet ready to proactively notify you, it's able to quickly deliver relevant, up-to-date information about the weather and financials.

Another new feature integrates the browser more closely with Microsoft's OneNote note-taking tool. You'll be able to annotate pages using ink (a feature that's focused on Microsoft's own Surface tablets) or by typing into a Web page, sharing the results as a Web note. You won't need Project Spartan to see shared Web notes. They can be saved into OneNote as an annotated screenshot of a Web page or emailed to contacts, with the added option of sharing to social networks.

Project Spartan's new annotation tools let you quickly add notes to a Web page, using a pen or a keyboard. You can then share your annotated Web page through social media or email -- or save it to OneNote as part of a research notebook.

Project Spartan improves on Internet Explorer's Reading View for viewing page content without distracting graphics or advertising, with a page layout that's easier to read. Reading View is also integrated with Project Spartan's Reading List (formerly a separate Windows 8 app). As offline reading won't arrive until a future build, you'll have to read saved pages while connected to the Internet. The final version will allow you to share your Reading List across devices, including Windows Phones and small tablets running a mobile version of Project Spartan.

Microsoft is putting Project Spartan front and center in Windows 10, with the new browser pinned to both the Start menu and the Windows task bar. You'll still be able to find IE, and if you've already pinned it, then it won't be removed. Microsoft recently announced that IE and Project Spartan would have separate rendering engines, and the change has now made its way to Windows with the Edge engine removed from IE in Windows 10 Build 10049. The old IE will remain part of Windows 10 (if only visible from All Apps) for businesses to use with legacy apps.

Web developers will find this build of Windows 10 to be useful for tuning sites and applications in preparation for Windows 10. You won't find any surprising new HTML or CSS features in this release. Project Spartan is based on the same version of the Edge engine used by IE in build 10041 with some minor additions, among them support for responsive images.

Developers will find the latest version of Microsoft's Web page debugging tools built into Project Spartan, which is handy for getting sites and applications ready for the launch of Windows 10 and the final version of Microsoft's new browser and rendering engine.

But as in IE of the previous build, there's support for much of ECMAScript 6, as well as Web Audio, CSS Gradient Midpoints, CSS Conditional Rules, and Touch Events. Now that Microsoft has divorced its new rendering engine from IE's Trident, Project Spartan will be where you'll find new Web technologies in the future, making it important to add the Windows 10 Technical Preview to Web test suites.

With only a week or so of development time separating this Windows 10 release from build 10041, Project Spartan is not merely the big news but the only news in this release. Apart from the new browser, there are only a handful of bug fixes in build 10049. Still, it's another step on the road to Windows 10's promised summer release.

Remember: This is still an early beta release of Project Spartan. On the HTML5Test, Project Spartan beats Internet Explorer 11 (375 to 336) but still lags the latest versions of Chrome (518), Opera (497), Firefox (449), and Safari (396). Much remains to be revealed before Windows 10 launches, including -- one hopes -- improved compatibility with HTML5.