$ perl -e 'printf "$_ => %b\n", ord($_) for qw( A B C @ )'
A => 1000001
B => 1000010
C => 1000011
@ => 1000000

##</code><code>##

"ABC" & "ABA" => "ABA"
"ABB" & "ABA" => "AB@"

"ABC" & "AB"  => "AB"
# perlop: "the & op acts as though the longer operand
# were truncated to the length of the shorter"
# so the strings don't have to be equal length
# for that to work