$aXML =~ s@</@{endtag}@gs;
  $aXML =~ s@/@{bs}@gs;
  $aXML =~ s@{endtag}@</@gs;
  $aXML =~ s@:@{colon}@gs;
  $aXML =~ s@;@{semicolon}@gs;

  ...

  $aXML =~ s@:;@\)\]@gs;
  $aXML =~ s@;([^:;]+?):@\[$1\(@gs;
  $aXML =~ s@`@>@gs;
  $aXML =~ s@{bs}@/@gs;
  $aXML =~ s@{colon}@:@gs;
  $aXML =~ s@{semicolon}@;@gs;

  ...

  while ($aXML =~ m@<([^<>]+?)>(.*?)</>@gs) { ... }

  ...

  while ($aXML =~ m@\[([^\[\]]*?)\]@gs) { ... }

##</code><code>##

  my @chars = split //, $aXML;

  ...

  foreach my $char (@chars) { ... }