def format_xml(self, value):
        """Render a formatted multi-line XML string from a complex Python
        data structure. Supports tag attributes and nested dicts/lists.

        :param value: Complex data structure representing XML contents
        :returns: Formatted XML string rendered with newlines and indentation
        :rtype: str
        """
        def normalize_iter(value):
            if isinstance(value, (list, tuple)):
                if isinstance(value[0], str):
                    xmlval = value
                else:
                    xmlval = []
            elif isinstance(value, dict):
                xmlval = list(value.items())
            else:
                raise TemplateRuntimeError(
                    'Value is not a dict or list. Cannot render as XML')
            return xmlval

        def recurse_tree(xmliter, element=None):
            sub = None
            for tag, attrs in xmliter:
                if isinstance(attrs, list):
                    for attr in attrs:
                        recurse_tree(((tag, attr),), element)
                elif element is not None:
                    sub = SubElement(element, tag)
                else:
                    sub = Element(tag)
                if isinstance(attrs, (str, int, bool, float)):
                    sub.text = six.text_type(attrs)
                    continue
                if isinstance(attrs, dict):
                    sub.attrib = {attr: six.text_type(val) for attr, val in attrs.items()
                                  if not isinstance(val, (dict, list))}
                for tag, val in [item for item in normalize_iter(attrs) if
                                 isinstance(item[1], (dict, list))]:
                    recurse_tree(((tag, val),), sub)
            return sub

        return Markup(minidom.parseString(
            tostring(recurse_tree(normalize_iter(value)))
        ).toprettyxml(indent=" "))