WPF TextBlock: boxselection and multi-line editing

This is my first challenge with WPF.

I'm looking into the possibility of having Bo开发者_运维问答x Selection and Multi-line editing on a WPF TextBox.

Do you know if it is possible and if someone has already build this? Any pointers into the right direction are very much appreciated!

Have a look to AvalonEdit: http://www.codeproject.com/KB/edit/AvalonEdit.aspx it is OS and very simple to interoperate.