#!/usr/bin/perl

use strict;
use warnings;

use XML::Twig;

my $t = XML::Twig->new( twig_handlers => { hl1 => \&fix_hl1,
                                           hl2 => \&fix_hl2,
                                           _all_ => \&fixup,
                                         }, 
                         keep_encoding => 1,
                         keep_spaces => 1,
                     )
                 ->parse( \*DATA);



sub fixup
  { my( $t, $elt)= @_;
    foreach my $pcdata ($elt->children( '#PCDATA'))
      { $pcdata->set_text( conv_chars( $pcdata->text)); } 
    $elt->flush unless( $_->in( 'hl1') || $_->in( 'hl2'));
  } 

sub conv_chars { my $t= shift; $t=~ s{—}{--}g; return $t; }
sub fix_hl1 { $_->set_tag( 'new_hl1')->prefix( 'fixed hl1:'); }
sub fix_hl2 { $_->set_tag( 'new_hl2')->prefix( 'fixed hl2:'); }

__DATA__
<!DOCTYPE nitf [
<!ENTITY foo "bar"> ]>
<nitf><s><hl1>hl1 with a &foo; and an other &foo; and &#8212; and &#8212;</hl1>
         <p>text, no foo</p>
         <p>text, no foo but &#8212;</p>
         <p>text, with &foo;</p>
         <hl2>hl2 with a &foo; and an other &foo; and &#8212; and &#8212;</hl2>
         <hl2>hl2 no foo </hl2>
         <hl2>hl2 with a bold <b>&foo;</b>, <b>&#8212;</b> and an other &foo;</hl2>
      </s>
</nitf>