Loads the contents for this walkthrough from XML.
        
        :param      xmlstr | <str>
        
        :return     <XWalkthrough> || None

def load(xmlstr):
        """
        Loads the contents for this walkthrough from XML.
        
        :param      xmlstr | <str>
        
        :return     <XWalkthrough> || None
        """
        try:
            xml = ElementTree.fromstring(xmlstr)
        except StandardError:
            return None

        return XWalkthrough.fromXml(xml)