From what I can tell, Ctrl+Shift+Z is slightly more common than Ctrl+Y (though both are frequently used) as a keyboard shortcut for Redo.
Not only does Ctrl+Shift+Z not work in the editor, but it actually interprets it as just Ctrl+Z, and thus invokes one further undo.
Assuming there's no intent to use Ctrl+Shift+Z for something else, I'd like to suggest that the editor accept either combination. At the very least, Ctrl+Shift+Z should not invoke undo.
