f() { for i; do echo "|$i|"; done; }

echo Unquoted 1:
x='1 2'; f a${x:+ 'x y' $x ''  "$x" `echo A B` "`echo C D`" z}b
echo Quoted 1:
x='1 2'; f "a${x:+ 'x y' $x ''  "$x" `echo A B` "`echo C D`" z}b"

echo Unquoted 2:
x='1 2'; f a${x:+'x y' $x ''  "$x" `echo A B` "`echo C D`" z }b
echo Quoted 2:
x='1 2'; f "a${x:+ 'x y' $x ''  "$x" `echo A B` "`echo C D`" z }b"

#echo Unquoted 3:
#e=
#x='1 2'; f a${x:+'x y' $x ''  "$x" $e $e "$e" $e `echo A B` "`echo C D`" z }b
#echo Quoted 3:
#x='1 2'; f "a${x:+ 'x y' $x ''  "$x" $e $e "$e" $e `echo A B` "`echo C D`" z }b"
