my %escapes = (
   '<'     => '&lab;',
   '>'     => '&rab;',
   '('     => '&lcb;',
   ')'     => '&rcb;',
   '['     => '&lsb;',
   ']'     => '&rsb;',
   '&lab;' => '<special>lab</special>',
   '&lcb;' => '<special>lcb</special>',
   '&lsb;' => '<special>lsb</special>',
   '&rab;' => '<special>rab</special>',
   '&rcb;' => '<special>rcb</special>',
   '&rsb;' => '<special>rsb</special>',
);

#my $escapes_pat = join '', map quotemeta, keys %escapes;
#my $escapes_re = qr/$escapes_pat/;
my $escapes_re = qr/[<>()\[\]]|&[lr][acs]b;/;  # Manually tweaked.

sub escape(_) {
   my ($s) = @_;
   $s =~ s/($escapes_re)/$escapes{$1}/g;
   return $s;
}

##</code><code>##

my %escapes = qw( & &AMP; < &LAB; > &RAB; ( &LCB; ) &RCB; [ &LSB; ] &RSB; );

sub escape(_) {
   my ($s) = @_;
   $s =~ s(/[&<>()\[\]])/$escapes{$1}/g;
   return $s;
}

##</code><code>##

my %escapes = qw( & &AMP; < &LAB; > &RAB; ( &LCB; ) &RCB; [ &LSB; ] &RSB; );

sub escape(_) { $_[0] =~ s(/[&<>()\[\]])/$escapes{$1}/gr }