title: Open Source Xml Editor
body: <p>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:</p>
  
  <ul>
  <li>XML Syntax Highlighting like VS</li>
  <li>Auto Completion</li>
  <li>Validation</li>
  </ul>
  
  <p>It's license should be that I can edit it and then release it, with the source code. </p>
  
  <p>Are there any things like that?</p>
  
  <p>Thanks.</p>