#sub captures {
#    local $_ = shift;
#    croak "$_ is not a compiled regexp" unless ref eq 'Regexp';
#    my $n = 0;
#    while( /\G(?=.)/gcs ) {
#      /\G[^\\(]*/gc;     # ignore uninteresting stuff
#      /\G(?:\\.)*/gc;    # ignore backslashed stuff
#      /\G\(\?/gc;        # ignore special regexps
#      /\G\(/gc && $n++;  # a capturing (, count it!
#    }
#    $n;
#}

sub captures { ( @_ = '' =~ /(@{[shift]})??/ ) - 1; }