my $re_start = qr/../; #match string begining with two of anything (0 or more times each!)
                       # but still a potential problem: would match a null string)
                      # so, perhaps, qr/.{1).(1)/ which will not allow a string 
                    # (preceding the comma in your initial set of regexen) 
                  # with anything other than two instances of something
                 #  or another

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"my $rx_dotdot = qr{ .. }xms;
 print 'A: match empty string' if '' =~ $rx_dotdot;
 ;;
 my $rx_counted = qr{ .{1}.{1} }xms;
 print 'B: match empty string: counted' if '' =~ $rx_counted;
 ;;
 print 'C: match empty string: counted, quantified'
   if '' =~ m{ $rx_counted? }xms;
"
C: match empty string: counted, quantified