This is one Silverlight 4 control I wanted to share. It extends the RichTextBox control in a way to add coloring of HTML and XML tags. The tags are colored as you type. I am planning also to add intellisense. It also has right click menu with Cut, Copy and Paste options for now but more can be added including custom links, activated by contextual position. Below you can see how a typical HTML looks when formatted:

This is the link to a demo page:

And here you can find the complete source code:

In the source code you will also see a full set of tests. To see the tests when you load the project go to the /Tests folder of the project web site.