API: If key begins with '@' treat it as an xml attribute

lib/api.php

@@ -188,18 +188,25 @@ class OC_API {
 	}
 
 	private static function toXML($array, $writer) {
+		
 		foreach($array as $k => $v) {
-			if (is_numeric($k)) {
+			if (substr($k, 0, 1) === '@') {
+				$writer->writeAttribute(substr($k, 1), $v);
+				continue;
+			} else if (is_numeric($k)) {
 				$k = 'element';
 			}
-			if (is_array($v)) {
+			
+			if(is_array($v)) {
 				$writer->startElement($k);
 				self::toXML($v, $writer);
 				$writer->endElement();
 			} else {
 				$writer->writeElement($k, $v);
 			}
+						
 		}
+		
 	}
 	
 }