Ex is the non-visual mode of vi, the mode that you are in when you type ":".
You can enter this mode semi-permanently by typing "gQ" (return to visual mode
Why would you want to do such a thing? Well, because if you are going to
do a bunch of ex mode commands in a row, and only care about seeing the results,
this is the way to do it. No more ":" to type, no waiting for the screen
to redraw. Ex is "line at a time" mode: if you search for
a pattern, only the first matching line displays. Press ENTER, and you see
the line below it. Let's look at an example with this file: