Can't call method "set_att" without a package or object reference at mine.pl line 40, <DATA> chunk 2.

##</code><code>##

#!/usr/bin/perl -w

use strict;

use XML::Twig;

$/="\n\n";

my $doc          = <DATA>;  # the original data set
my $expected_doc = <DATA>;  #  result with elements changed to attributes

my $twig= new XML::Twig(                    # create the twig
			pretty_print => 'indented', 
			twig_roots   => 
			      { 
			       'elt_att'  =>   sub { addAtt(@_,'elt') }, 
			       'selt_att' =>   sub { addAtt(@_,'subelt') },  
			      },
			  );   


  $twig->parse($doc);
  $twig->flush;


# Finished.
exit(0);

# Give a decent error message if we wrote to stdout and had disk full.
END { close(STDOUT) || die "ERROR: can't close stdout: $!\n" }

#===============================================================================
# Subroutines
#-------------------------------------------------------------------------------


sub addAtt
  { my( $t, $att,$parent)= @_; 
    my $e_parent = $t->findnodes($parent);
    $e_parent->set_att($att->gi,$att->trimmed_text);
    $att->delete;
    $t->flush;            
}


__DATA__
<doc>
  <elt elt_class="class1">
    <subelt subelt_class="sclass1"><content id="content1"/></subelt>
    <elt_att att="elt_att1"></elt_att>
  </elt>
  <elt elt_class="class2">
    <subelt subelt_class="sclass2"><content id="content2"/></subelt>    
    <selt_att att="selt_att1"></selt_att>
  </elt>
  <elt elt_class="class3">
    <subelt subelt_class="sclass3"><content id="content3"/></subelt>
    <elt_att att="elt_att1"></elt_att>
  </elt>
</doc>

<doc>
  <elt elt_class="class1" elt_att="elt_att1">
    <subelt subelt_class="sclass1">
      <content id="content1"/>
    </subelt>
  <elt elt_class="class2">
    <subelt subelt_class="sclass2" selt_att="selt_att1">
      <content id="content2"/>
    </subelt>
  </elt>
  <elt elt_class="class3"  elt_att="elt_att1">
    <subelt subelt_class="sclass3">
      <content id="content3"/>
    </subelt>
  </elt>
</doc>