I find this shortcut extremely useful in Xcode: duplicate one or several lines without losing what you have on the clipboard.
- To add custom key bindings in Xcode, you have to edit this file (su privileges required):
/Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Versions/Current/Resources/IDETextKeyBindingSet.plist
I add the following new key at the bottom: