Customising word separators in vi

Question

vi treats dash - and space   as word separators for commands such as dw and cw.

Is there a way to add unders

Answer 1

You could type cf_dest_ and save the counting part.

Edit: or as suggested: ct_ changes text until right before the underline character. (I'm using the f motion more, so it came more naturally to me)

Or you could redefine 'iskeyword' (:help iskeyword for details).