set -- ' abc' 'def ghi' 'jkl '

echo normal IFS
recho $@
: ${var=$@}
recho $var
unset -v var
recho ${var-$@}

echo null IFS
IFS=
recho $@
: ${var=$@}
recho $var
unset -v var
recho ${var-$@}

echo non-standard IFS
IFS=:
recho $@
: ${var=$@}
recho $var
unset -v var
recho ${var-$@}	# this is inconsistent

echo unset IFS
recho $@
: ${var=$@}
recho $var
unset -v var
recho ${var-$@}
