Editing (8)
'editing' is the definition.
(I know that revision is a type of rewriting)
This is all the clue.
(Other definitions for revision that I've seen before include "It's done before examination" , "Improving change" , "Preparation for exam" , "Study of notes, etc, before exam" , "Cramming (for exam)" .)
(Other definitions for emending that I've seen before include "Removing errors and making improvements" , "... putting things right" , "Setting right, correcting" .)