Version 2013.4 and forward will use Visual Studio 2012 as the main IDE from now on(But you should still be able to compile in VS 2010 though, just create a new WPF project and import all of the files). It will also be the last version with ClickOnce support.
What's new for Document.Editor 2013.4:
Improved FTP Export dialog
Improved Spell Check
Minor Bug Fix's, improvements and speed ups