G'day Monks, I am struggling in XML::Twig for increment the tag content.

use strict;
use warnings;
use XML::Twig;
use XML::XPath;
use XML::Twig::XPath;

my $twigrp = new XML::Twig::XPath(    pretty_print   => 'indented_c', 
+           # print format
                                                                      
+  keep_encoding  => 1,
                                                                    );
$twigrp->parse(\*DATA);    

my %insbeforetag;
$insbeforetag{1} = [('//chbody//exercises/orderedlist/item/para', 'ins
+t', '\t{{Num}\.\t')];

for my $row (keys %insbeforetag){
    for ($twigrp->findnodes($insbeforetag{$row}->[0]))
    {
        my $min_elt= XML::Twig::Elt->new( $insbeforetag{$row}->[1] => 
+$insbeforetag{$row}->[2]); 
        $min_elt->paste( before => $_);
    }
}

$twigrp->print;

__DATA__
<chapter>
<chbody>
<exercises att="problems">
<title>Content</title>
<orderedlist numeration="number">
<item><para>Text1</para></item>
<item><para>Text2</para></item>
<item><para>Text3</para></item>
</orderedlist>
<orderedlist numeration="number">
<item><para>Text1</para></item>
<item><para>Text2</para></item>
<item><para>Text3</para></item>
<item><para>Text4</para></item>
</orderedlist>
</exercises>
</chbody>
</chapter>
[download]

Output as:

<chapter>
  <chbody>
    <exercises att="problems">
      <title>Content</title>
      <orderedlist numeration="number">
        <item>
          <inst>\t{{Num}\.\t</inst>
          <para>Text1</para></item>
        <item>
          <inst>\t{{Num}\.\t</inst>
          <para>Text2</para></item>
        <item>
          <inst>\t{{Num}\.\t</inst>
          <para>Text3</para></item></orderedlist>
      <orderedlist numeration="number">
        <item>
          <inst>\t{{Num}\.\t</inst>
          <para>Text1</para></item>
        <item>
          <inst>\t{{Num}\.\t</inst>
          <para>Text2</para></item>
        <item>
          <inst>\t{{Num}\.\t</inst>
          <para>Text3</para></item>
        <item>
          <inst>\t{{Num}\.\t</inst>
          <para>Text4</para></item></orderedlist></exercises></chbody>
+</chapter>
[download]

But expected Output as:

<chapter>
<chbody>
<exercises att="problems">
<title>Content</title>
<orderedlist numeration="number">
<inst>    1.    </inst><item><para>Text1</para></item>
<inst>    2.    </inst><item><para>Text2</para></item>
<inst>    3.    </inst><item><para>Text3</para></item>
</orderedlist>
<orderedlist numeration="number">
<inst>    1.    </inst><item><para>Text1</para></item>
<inst>    2.    </inst><item><para>Text2</para></item>
<inst>    3.    </inst><item><para>Text3</para></item>
<inst>    4.    </inst><item><para>Text4</para></item>
</orderedlist>         
</exercises>           
</chbody>
</chapter>
[download]

Tag content as "\t{{Num}}\.\t" will be " 1. " with orderedlist sequence. Each orderedlist {{Num}} will be reset. How to achive this?

Thanks in advance.