perl: REGEX help

Hi I need to test meta data keys for valid
These Formats are valid

geo.0123.lowercaseword
AB.lowercaseword.lowercaseword
AB.lowercaseword.123
ABC.lowercaseword123
ABC.lowercaseword.lowercaseword
exception(s) or special cases where above rules don't apply

not valid
ab.UPPERcaseword123
AD.not132valid


so unless geo or exception
2 or 3 uppercase letters DOT lowercaseword DOT or numbers

for my $metaKey (sort keys $metaHash){
  next if($metaKey =~ m/(exceptions|list/);
  if($metaKey =~ m/^([A-Z]{2,3}\.[a-z0-9|\.]|geo\.\d.*[a-z])$/{
      print "$metaKey good\n";

  }
  else{
     print "$metaKey bad\n";

  }
}

I suspect I'll need to do this in 2 goes as the exceptions list might be quite long but if the $metaKey is not in this list or it's the wrong format it's bad

I'm assuming a hash key is case sensitive
so "HashKey" is not the same as "hashkey" and 1 doesn't overwrite the other?