As long as an edit remains 'unsaved', Ctrl+z will UNDO any changes; Ctrl+y will REDO.
Before editing a file, if you want to retain an unedited and original version, Left Click ONCE on it, Ctrl+c (Copy) then Ctrl+v (Paste) and work on the copy.
More compression and other info here.
Okay; THIS time I don't know what I have
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