I, also, don't really understand the requirements | vaguely-stated requirements of the OP. The way I'd like to see a question like this posted (and a way that'd be more likely to get useful responses IMHO) is something like: 

c:\@Work\Perl\monks>perl -wMstrict -le
"use Test::More 'no_plan';
 use Test::NoWarnings;
 ;;
 use constant TEST_ACCEPT => qw(
   {12}  {1b}  {a2}  {ab}
   {12_34}  {1b_34}  {a2_34}  {ab_34}  {12_3d}  {1b_c4}  {a2_cd}
   {aa_bb_cc_dd_ee}  {a1_11_1c_bb}
   {aaa}  {a}
   );
 ;;
 use constant TEST_REJECT => qw(
   {a_bb_cc_dd_ee}  {aaa_bb_cc_dd_ee}  {1_11_1c_bb}  {123_11_1c_bb}
   {aa_}  {a_}  {_aa}  {_a}
   {1}  {123}  {abc1}  {_}
   );
 ;;
 my $rx_scored = qr{ [[:alnum:]]{2} (?: _ [[:alnum:]]{2})* }xms;
 my $rx_alphas = qr{ [[:alpha:]]+ }xms;
 ;;
 my $rx = qr{ \A \{ (?: $rx_scored | $rx_alphas) \} \z }xms;
 ;;
 note 'all to be accepted';
 ;;
 for my $string (TEST_ACCEPT) {
   ok $string =~ $rx, qq{accept '$string'};
   }
 ;;
 note 'all to be rejected';
 ;;
 for my $string (TEST_REJECT) {
   ok $string !~ $rx, qq{reject '$string'};
   }
 ;;
 done_testing;
"
# all to be accepted
ok 1 - accept '{12}'
ok 2 - accept '{1b}'
ok 3 - accept '{a2}'
ok 4 - accept '{ab}'
ok 5 - accept '{12_34}'
ok 6 - accept '{1b_34}'
ok 7 - accept '{a2_34}'
ok 8 - accept '{ab_34}'
ok 9 - accept '{12_3d}'
ok 10 - accept '{1b_c4}'
ok 11 - accept '{a2_cd}'
ok 12 - accept '{aa_bb_cc_dd_ee}'
ok 13 - accept '{a1_11_1c_bb}'
ok 14 - accept '{aaa}'
ok 15 - accept '{a}'
# all to be rejected
ok 16 - reject '{a_bb_cc_dd_ee}'
ok 17 - reject '{aaa_bb_cc_dd_ee}'
ok 18 - reject '{1_11_1c_bb}'
ok 19 - reject '{123_11_1c_bb}'
ok 20 - reject '{aa_}'
ok 21 - reject '{a_}'
ok 22 - reject '{_aa}'
ok 23 - reject '{_a}'
ok 24 - reject '{1}'
ok 25 - reject '{123}'
ok 26 - reject '{abc1}'
ok 27 - reject '{_}'
1..27
ok 28 - no warnings
1..28

[download]
Of course, one would omit the test regex or use a dummy in an initial query post.

Give a man a fish:  <%-{-{-{-<

In reply to Re: Looking for a regular expression for the following pattern. by AnomalousMonk
in thread Looking for a regular expression for the following pattern. by skooma

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