How to use the doc8.utils.filtered_traverse function in doc8

def find_line(node):
            n = node
            while n is not None:
                if n.line is not None:
                    return n.line
                n = n.parent
            return None

        def filter_systems(node):
            if utils.has_any_node_type(node, (docutils_nodes.system_message,)):
                return False
            return True

        nodes_lines = []
        first_line = -1
        for n in utils.filtered_traverse(doc, filter_systems):
            line = find_line(n)
            if line is None:
                continue
            if first_line == -1:
                first_line = line
            contained_lines = set(gather_lines(n))
            nodes_lines.append((n, (min(contained_lines), max(contained_lines))))
        return (nodes_lines, first_line)