Sorry for totally off-topic question.
I seem to remember that there’s a way to have vim display only certain
lines in the buffer, like those satisfying a pattern. Unfortunately, I
do not remember how to turn it on and all my attempts to find the
information failed miserably. I vaguely remember that the mode was
called something like “condensed display” or “compact display” or
“compressed display” (I searched for everything, all in vain).
Does anybody know how to do it? Any hint will be greatly appreciated.