##

use strict;
use warnings;
use XML::LibXML;

my $reader = XML::LibXML->load_xml(location => "test.xsl") or die "cannot read input file\n";
my $xpath_context = XML::LibXML::XPathContext->new($reader);

foreach my $element_node ($xpath_context -> findnodes('//xsl:element')) {
my @attributes = $element_node -> attributes();
$element_node -> setNodeName($attributes[0]);
}