If used the means to debug are next to 0 without editing the code (to remove the @-operator).

--- library/Zend/Dom/Query.php  (revision XXX)
+++ library/Zend/Dom/Query.php  (working copy)
@@ -176,12 +176,12 @@
         $type   = $this->getDocumentType();
         switch ($type) {
             case self::DOC_XML:
-                $success = @$domDoc->loadXML($document);
+                $success = $domDoc->loadXML($document);
                 break;
             case self::DOC_HTML:
             case self::DOC_XHTML:
             default:
-                $success = @$domDoc->loadHTML($document);
+                $success = $domDoc->loadHTML($document);
                 break;
         }

It should be left to the developer to catch E_WARNING instead. There's multiple ways, e.g. an error handler to generate an exception or a simple log file, etc..

This should be added to the Coding Standards as well so people avoid this kind of thing in other components.