This means that a script containing:
echo 1
set -v
echo 2
will now produce output, like it does on SYSV machines and other 'proper'
/bin/sh implementations..
This is done by a slight restructure of the input processor allowing it to
read chunks from the file at a time, but process the data by line from the
chunk.
Obtained from: Christos Zoulas for NetBSD. <christos@deshaw.com>