In a SVG generated with Graphviz, this adds a xlink in the text node element

graphviz-svg-add-xlink

<?php
$xml = simplexml_load_file($argv[1]);
$xml->registerXPathNamespace('s', 'http://www.w3.org/2000/svg');
$objs = $xml->xpath("/s:svg/s:g[@id='graph1']/s:g[@class='node']/s:text");
foreach($objs as &$v) {
	$text = (string)$v[0];
	$v[0] = null;
	$a = $v->addChild("a", "{$text}");
	$a->addAttribute("xlink:href", "{$text}.html", "http://www.w3.org/1999/xlink");
}
$xml->asXML("done_".$argv[1]);
?>