#!/bin/perl -w
use strict;

use XML::Twig;

my $t= new XML::Twig( # called for all opening tags
                 start_tag_handlers => { _all_ => \&store_position },
                 # called for each closing elt tag
                  twig_handlers      => { elt => \&elt});
$t->parse( \*DATA);

sub store_position
  { my( $t, $elt)= @_;
    my $line   = $t->{twig_parser}->current_line;            # $t->{twig_parser} is the expat object
    my $column = $t->{twig_parser}->current_column;
    $elt->{my_atts}= { line => $line, column => $column };   # crude but works
  }


sub elt
  { my( $t, $elt)= @_;
    if( my $error= $elt->att( 'error'))
      { my $line   = $elt->{my_atts}->{line};
        my $column = $elt->{my_atts}->{column};
        print STDERR "error $error at $line:$column\n";
       }
  }

__DATA__
<doc>
  <elt>this one is OK</elt>
  <elt error="foo">not this one though</elt>
  <elt>OK</elt>
  <elt error="bar">here is a bar error</elt>
</doc>