Microsoft has spent the past few days talking about the new browser formerly known as Project Spartan: what it will do, what it won’t do, and what it won’t do yet but will do soon.

We already knew that Microsoft Edge would remove much of the legacy technology that’s found in Internet Explorer. Microsoft has given perhaps the fullest rundown of what’s not in Edge this week. The two traditional ways of extending Internet Explorer, ActiveX and Browser Helper Objects, are both gone. This means no plugins, no toolbars, no Java, no Silverlight. It doesn’t, however, mean no Flash; that’s a built-in capability. PDF rendering is also built-in.

In their place are Chrome-like extensions built in HTML and JavaScript. However, these aren’t coming immediately. Although Microsoft has demonstrated the popular Reddit Enhancement Suite running in Edge with (the company says) minimal changes from its Chrome version, the initial release of Edge won’t support these extensions. There’s no specific timeline on when they’ll be added.

The new extensibility support will be quite broad. Internet Explorer currently has lots of extension points for developers; they can add, for example, custom download managers, custom protocol handlers, context menu entries, sidebars, and security filters. All of these and more will be handled by the new extensibility system when it’s available.

The company has also said that it has a “long-term goal” of bringing extension support to its mobile browser, though initial support will be for PC only. More specifically, it will be for Windows 10 only. There are “no plans” to make the browser (or its core engine) open source, and doing so would apparently come at “massive cost.”

Unlike Internet Explorer, Edge won’t try to mimic older browsers in order to work around page bugs and glitches. This means that document modes and layout quirks are both gone. Edge will always be at the cutting edge, offering Microsoft’s newest take on Web standards. This commitment to standards also means that various non-standard technologies are being removed: Edge won’t support VML vector graphics, VBScript scripts, DirectX filters and transitions, or non-standard scripting techniques for responding to events or accessing CSS styling.

Read More: All about Edge: Extensions, high performance asm.js, and no more ActiveX | Ars Technica.