I need to write a XML-based markup language. I'd like to provide an open source IDE for it, but I don't want to write it from scratch. So, I'm looking for an open source XML editor, written in C#, with WinForms or WPF UI, which I'll can extend it and add my markup language validation and etc, with the following features:
It's license should be that I can edit it and then release it, with the source code.
Are there any things like that?
Thanks.