use warnings;
use strict;
use XML::LibXML;
my $doc = XML::LibXML::Document->new;
my $el1 = $doc->createElementNS("namespace0","aaa");
$el1->setNamespace("namespace1","p1",0);
$el1->setNamespace("namespace2","p2",0);
$doc->setDocumentElement($el1);
my $el2 = $doc->createElement("bbb");
$el2->setNamespace("namespace2","p2",1);
$el1->appendChild($el2);
my $el3 = $doc->createElementNS("namespace0","ccc");
$el1->appendChild($el3);
my $el4 = $doc->createElement("p1:ddd");
$el3->appendChild($el4);
print $doc->toString(1);

__END__

<?xml version="1.0"?>
<aaa xmlns="namespace0" xmlns:p1="namespace1" xmlns:p2="namespace2">
  <p2:bbb/>
  <ccc>
    <p1:ddd/>
  </ccc>
</aaa>