This is not a problem. You may set DOMDocument's documentURI property.
Something like this
$xsl = new DOMDocument('1.0','UTF-8');
$xsl->documentURI = '/foo/bar/somefile.xsl';
$xslProc = new XSLTProcessor();
and document('other.xsl') will work fine!
PHP5 xsl processor has a different behaviour than PHP4's one with CDATA sections. (see http://bugs.php.net/bug.php?id=29837)
Loaded XSL sheet CDATA sections does not allow, by default, output-escaping handling (everything in the CDATA is escaped by default).
So in this case you can't build your XSL Dom the usual way:
$xsldom = DomDocument::loadXML(file_get_contents('sheet.xsl'));
and must go through this one (allowing LIBXML_NOCDATA parameter):
$xsldom = new DomDocument;
Then the CDATA output-escaping behaviour will be correct.
For those who wants to use external documents, it is important not to use the DomDocument::loadXML because the processor will not have the path to look for other files
So if you want to transform some xml with a pre-generated stylesheet $f:
$f = 'somestylesheet.xsl';
$xsl = DomDocument::loadXML(file_get_contents($f));
document('other.xml') will not work with relative path and
$xsl = DomDocument::load($f);