set -- '1 2'

unset var
recho ${var-${*:1}}

unset var
recho ${var=$*}

unset var
recho ${var=${*:1}}
recho "$var"

# posix interp 221
unset var
recho ${var:-a\ b}

recho ${var:=a\ b}
recho "$var"

set -- 1 2
IFS=

unset a b c
recho $*
recho ${a-$*}
recho ${b-${*/}}
recho ${c=${*/}}
recho "$c"
recho ${b-${*,,}}
recho ${d-${*,,}}

unset -v a b c
IFS=$' \t\n'

set -- ' '
A=(' ')

IFS=
unset var
var=${*@E}
recho "$var"

unset var
var=${A[*]@E}
recho "$var"

unset var
var=${@@E}
recho "$var"

unset var
var=${A[@]@E}
recho "$var"

unset novar
recho ${novar-${A[*]@E}}

unset -v var novar
IFS=$' \t\n'

set -- 1 2
A=( 1 2 )
IFS=

a=$* 
recho "$a"
b=${*@E}
recho "$b"

unset a b
a=${A[*]}
recho "$a"
b=${A[*]@E}
recho "$b"

set -- $'\t'
A=$1

IFS=$1
[[ ${A[@]} ]] && echo ok 1
[[ ${A[*]} ]] && echo ok 2
[[ ${A[0]} ]] && echo ok 3

IFS=$' \t\n'
[[ ${A[@]} ]] && echo ok 4
[[ ${A[*]} ]] && echo ok 5
[[ ${A[0]} ]] && echo ok 6

IFS=
[[ ${A[@]} ]] && echo ok 7
[[ ${A[*]} ]] && echo ok 8
[[ ${A[0]} ]] && echo ok 9