-r is now repeatable and restrictive: unit specs (l/s/v/r) intersect
their database line windows, while plain-number specs index into the
filtered output items left after unit windows and --grep, acting as a
pure display filter (negatives from the end, single index errors with
exit 2, ranges truncate). --context N (default 0) then expands each
surviving item GNU grep-style by N surrounding in-window records, free
of the grep/plain filters, merging overlaps.
LeoVasanko