Pass URL as a parameter to XSL

I'd like to pass current page URL as an attribute to XSL template. As far as I understood it should be passed as a parameter, and then used as an attribute.

I use PHP to load XML & XSL files:

<?php
$xml = new DOMDocument;
$xml->load('main.xml');

$xsl = new DOMDocument;
$xsl->load('blocks/common.xsl');

$proc = new XSLTProcessor;

$proc->importStyleSheet($xsl);

echo $proc->transformToXML($xml);
?> 

How should this code be altered to pass URL as a parameter named "current-url", for example?

I've seen a lot of similar questions here with different solutions, but none has worked for me so far. Thank you in advance.