Register xs+xml namespaces

Author: tvdijen

src/Utils/XPath.php

@@ -8,6 +8,7 @@
 use DOMNode;
 use DOMXPath;
 use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Constants as C;
 
 /**
  * XPath helper functions for the XML library.
@@ -37,6 +38,9 @@ public static function getXPath(DOMNode $node): DOMXPath
             $xpCache = new DOMXPath($doc);
         }
 
+        $xpCache->registerNamespace('xml', C::NS_XML);
+        $xpCache->registerNamespace('xs', C::NS_XS);
+
         return $xpCache;
     }