Return a list of all the matched tags in all available xml

        :param str tag: specify the tag name

def find_tags(self, tag_name, **attribute_filter):
        """
        Return a list of all the matched tags in all available xml

        :param str tag: specify the tag name
        """
        all_tags = [
            self.find_tags_from_xml(
                i, tag_name, **attribute_filter
            )
            for i in self.xml
        ]
        return [tag for tag_list in all_tags for tag in tag_list]