use XML::LibXML;

my $string = q|
<Root>
<A >
  <B>B value</B>
    <C>
        <D d_attribute="d_attribute_value">D_Value</D>
    </C>
</A >
<A>
  <B>B value</B>
    <C>
        <D d_attribute="d_attribute_value">D_Value</D>
    </C>
</A>
</Root>
|;

my $doc = XML::LibXML->load_xml(string => $string);

my @B = $doc->findnodes("//A/B");
if (@B) {
	for my $node (@B) {
		my $val = $node->textContent;
		print qq|Value of B is: $val\n|;
	}
}

my @D = $doc->findnodes("//A/C/D");
if (@D) {
	for my $node (@D) {
		my $attr = $node->getAttribute("d_attribute");
		print qq|Attribute 'd_attribute' of D is: $attr\n|;
		my $val = $node->textContent;
		print qq|Value of D is: $val\n|;
	}
}