while ( <FILE> ) {
  if ( isPrimary() ) {
    push @primary, $_; 
  } elsif ( isSecondary() ) {
    push @secondary, $_;
  } elsif ( isTertiary() ) {
    push @{$secondary[$#secondary]}, $_;
  }
 }

 @primary = sort { $a cmp $b } @primary;
 @secondary = sort { $a cmp $b } @secondary;
 
 foreach $secondaryItem ( @secondary ) {
  @{$secondaryItem} = sort { $a cmp $b } @$secondaryItem;
 }