http://msdn.microsoft.com/en-us/library/bb787873%28v=vs.85%29.aspx
That exact link is the real documention about rich edit control (remember, the script editor have one and each channel's editboxes are rich edit control too).
I invite you to scroll down until you can see
Quote:
Ctrl+Z Undo
Ctrl+Y Redo
Now, see your screenshot ? Why don't you do the same with the script editor and realize control + y is just nicely written next to "redo" ?


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