Using the SAX interface

Given (1) a simple document:

<Dok>
   <E>1</E>
   <E>2</E>
   <E>3</E>
   <E>4</E>
   <E>5</E>
   <E>6</E>
   <E>7</E>
   <E>8</E>
   <E>9</E>
   <E>10</E>
   <E>11</E>
   <E>12</E>
   <E>13</E>
</Dok>

(2) a simple requirement to transform it via SAX (imaginary giant
input document) to the following:

<Dok>
   <Gr>
     <E>1</E>
     <E>2</E>
     <E>3</E>
     <E>4</E>
     <E>5</E>
     <E>6</E>
   </Gr>
   <Gr>
     <E>6</E>
     <E>7</E>
     <E>8</E>
     <E>9</E>
     <E>10</E>
     <E>11</E>
   </Gr>
   <Gr>
     <E>11</E>
     <E>12</E>
     <E>13</E>
   </Gr>
</Dok>

How would I proceed in Perl?

I seem to have very basic beginner problems. Here's what I have so far:

use strict;
use warnings;
use XML::SAX::ParserFactory;
use XML::SAX::Writer;

my $xmlfile = shift or die 'Zu parsendes Dokument uebergeben!';
my $filter = Gurke->new(Handler => XML::SAX::Writer->new);
$XML::SAX::ParserPackage = 'XML::LibXML::SAX';
my $parser = XML::SAX::ParserFactory->parser(Handler => $filter);

eval { $parser->parse_file($xmlfile) };
die "parse_file($xmlfile) : $@" if $@;

package Gurke;
use base 'XML::SAX::Base';

sub start_element {
     my($self, $data) = @_;
     $self->SUPER::start_element($data);
}

The output I get when processing the XML document shown above is:

<?xml version="1.0"?>
<Dok>
   <E>1</E>
   <E>2</E>
   <E>3</E>
   <E>4</E>
   <E>5</E>
   <E>6</E>
   <E>7</E>
   <E>8</E>
   <E>9</E>
   <E>10</E>
   <E>11</E>
   <E>12</E>
   <E>13</E>
</Dok>IO::Handle=IO(0x81532f4)

What's that stringified object reference doing there at the end?

When I change start_element() to only print the element names:

sub start_element {
     my($self, $data) = @_;
     print $data->{Name}, "\n";
}

I get the following output (STDOUT and STDERR combined):

<?xml version="1.0"?>
Dok
E

   1</E>E

parse_file(sax.xml) : Trying to pop context without push context at 
/usr/share/perl5/XML/NamespaceSupport.pm line 79. at 
/usr/local/lib/perl/5.8.8/XML/LibXML/SAX.pm line 64
  at sax.pl line 12
   2</E>

Searching for "Trying to pop context without push context" led me to:

http://osdir.com/ml/lang.perl.xml/2003-10/msg00029.html

But I don't have two documents here, I have only one.

How is this SAX API supposed to be used?

How would I go about solving the task outlined above?

Michael Ludwig
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