#!/usr/bin/perl -w

"abcde" =~ /(..)(?:(....)|(..))/;
# $1 is 'ab'
# $2 is undef
# $3 is 'cd'

print length($2);

##</code><code>##

#!/usr/bin/perl -w

print length($foo);

##</code><code>##

/* n is the number in $N */

if (
  (n <= rx->nparens) &&
  (s = rx->startp[n]) != -1 && /* -1 => not there */
  (e = rx->endp[n])   != -1
) return e - s;
return 0;