Recursive loop over DDXMLDocument objective-c

I would like to loop recursively over DDXMLDocument, and to change the elements attributes.

How can I do it ? I currently have the document and the root element:

DDXMLDocument *theDocument = [[DDXMLDocument alloc] initWithXMLString:content options:0 error:&error];
    DDXMLElement *rootElement = theDocument.rootElement;

postfix tree walk implemented:

-(void)processNode:(DDXMLNode *)node {
    if(node.kind == DDXMLElementKind) {
       //...
       for(DDXMLNode *child in node.children) {
           [self processNode:child];
       }
    }
}