More rumored details are leaking about Microsoft's new browser, codenamed "Spartan," that will be a key piece of its Windows 10 platform.

Spartan, a new Microsoft browser that will use the Trident rendering engine and the Chakra JavaScript engine that are part of Internet Explorer, is not just another new IE release, sources told me a week or so ago. Spartan is expected to look and work more like lightweight browsers such as Google's Chrome and Mozilla's Firefox, sources have said. It allegedly will support extensions, unlike IE.

This week, there was a BGR report and alleged Spartan screen shot (the screen shot was likely a fake, my sources say) which claimed Spartan would be integrated with Microsoft's Cortana personal digital assistant technology. One of my contacts say this is accurate information, and Tom Warren at The Verge is hearing the same as well.

Given that Microsoft is building Cortana support into Windows 10 (both desktop and the coming mobile release for smaller tablets and Windows Phones), Cortana integration makes a lot of sense. On phones, especially, the ability to tell a browser to "Go to Facebook," or "Check the Status of British Air Flight 103," would be handy.

The Verge's Tom Warren is reporting that Spartan will include digital inking support "that allows Windows 10 users to annotate a web page with a stylus and send the notes and annotations to a friend or colleague." Annotated Web pages will be able to be stored in OneDrive "that can be accessed by any browser across multiple platforms," Warren said.

Warren also said he has heard Spartan will allow users to group tabs however they want, splitting work and personal tabs if they so desire. One of my contacts confirmed there will likely be a "grouped tabs" feature in Spartan to help users better maintain the context of where links came from. Spartan may allow users to open multiple sites in grouped tabs together, which would allow users to do things like compare prices of a new phone without having to switch between tabs, my source said.

On Neowin, Brad Sams posted earlier this week a mock up based on what he said were actual screen shots of an early version of Spartan. One of my sources said that this screen shot and mock up accurately reflect how Spartan is evolving from a user interface standpoint. However, because Spartan was designed using many of the new UI design elements for Windows 10 that haven't yet been released publicly, it's hard to get an accurate picture right now of what Spartan ultimately may look like, one of my contacts said.

Neowin's Sams also noted that Spartan would replace "Modern" IE, a k a the Windows Store/Metro Style IE variant that was part of Windows 8. The Verge's Warren said he's also hearing Spartan will be a Windows Store app -- and one that will actually be downloadable from the Store.

Right now, IE isn't an app that Windows 8 or Windows Phone users get via the Windows Store or Windows Phone Store; it's part of the OS platform. By making Spartan an app, Microsoft should be able to update it more quickly.

As I noted a week or so ago -- but which a number of bloggers and reporters who covered my post misreported -- Microsoft is not killing IE and replacing it with Spartan. IE will remain an option available for Windows 10 PCs and desktops for users who want and need it. But Spartan will be installable and work on Windows 10 PCs, desktops, tablets and phones.

An interesting aside: One of the reasons Spartan is still using Trident (and not an alternative like Webkit) is to help with site compatibility. If Spartan detects a site was written for an old version of IE, it can use Trident to render it like IE would, one of my contacts said.

Microsoft is expected to show off and discuss Spartan at least to some extent during the January 21 Windows 10 preview event it is holding in Redmond.