If you don't need a single regex to do all the work then something like the following might prove useful:
use strict;
use warnings;

my $string = 'A000 A123 A567 B789 B888 B999 B000 A998 A999';

my $regex = qr/((A|B)(\d{3}))/;
while  ( $string =~ /$regex/g ) {
  if ( $2 eq 'A' ) {
    if ( $3 == 000 or 
        ($3 >= 123 and $3 <= 456) or $3 == 999 ) {
    print "$1 valid string\n"; }
    else { print "$1 rejected invalid range\n" }
  }
  elsif ( $2 eq 'B' ) {
    if ( $3 == 000 or ($3 >= 789 and $3 <= 888) ) {
      print "$1 valid string\n"; 
    }
    else { print "$1 rejected invalid range\n" }
  }
  else { print "$3 seems valid to me\n" }
}

[download]

update:
something else along the same lines:

while  ( $string =~ /((?:A|B)\d{3})/g ) {
  if ( $1 eq 'A000' or 
       ( $1 ge 'A123' and $1 le 'A456' ) or
       ( $1 ge 'A999' and $1 le 'B000' ) or
       ( $1 ge 'B789' and $1 le 'B888' )
      ) {
     print "$1 matched\n";
       }
  else { print "$1 did not match\n" }

[download]
or if you are going only for regex only solutions according to this the following regex should be valid in both: 
/(A(?:000|(?:1(?:2[0-3]|[01]\d))|[23]\d{2}|4(?:[0-4]\d|5[0-6])|999)|B(
+?:000|789|79\d|(?:8[0-7]\d|88[0-8]+)))/

[download]

-enlil

In reply to Re: Need Set-like Regex for Perl and Java (golf OK) by Enlil
in thread Need Set-like Regex for Perl and Java (golf OK) by QM

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