So AvalonEdit is licensed under GNU Library General Public License (LGPL). I have made my own modification to the library's source code. I understand that I have to release the modified source code. My questions are:
Only AvalonEdit 4.x is LGPL; in 5.x we re-licensed to MIT.
1. Modifications to LGPL code must also be LGPL.
2. Don't remove the existing copyright notice. Feel free to add your own copyright notice in addition.