Actipro has a WPF MGrammar syntax editor

http://www.actiprosoftware.com/Products/DotNet/WPF/SyntaxEditor/Default.aspx

I haven’t tried to use this yet but it seems pretty interesting.

SyntaxEditor is a powerful text editing control that is packed with features for efficient code editing, including syntax highlighting, line numbers, block selection, IntelliPrompt UI, split views, zooming, bi-di support, and much more. It has many of the same code editing features found in the Visual Studio code editor.

SyntaxEditor is built on top of our next-generation extensible text/parsing framework. While over 20 sample languages are available to get you started (such as C#, VB, XML, and more), custom language definitions can be developed and distributed with your applications as well. SyntaxEditor is designed for use in IDE (integrated development environment) applications, however there are many other applications out there than can take advantage of such a control.

A free add-on is included that integrates domain-specific language (DSL) parsers created using Microsoft Olso's MGrammar with SyntaxEditor, allowing it to syntax highlight code based on the DSL parser.