print length pack '(A2)*', 'fr','ed','x';;
6

print unpack 'C*', pack '(A2)*', 'fr','ed','x';;
102 114 101 100 120 32

print length pack '(a2)*', 'fr','ed','x';;
6

print unpack 'C*', pack '(a2)*', 'fr','ed','x';;
102 114 101 100 120 0

print length pack '(Z2)*', 'fr','ed','x';;
6

print unpack 'C*', pack '(Z2)*', 'fr','ed','x';;
102 0 101 0 120 0  ## Note! the 'r' & 'd' characters have been thrown away? Another bug?