def flatten(tokens, endings, base_path):
    """
    Used by

    - parse.map.blocks
    - parse.map.objects
    - parse.tileset.gfx
    - parse.spriteseheet.gfx
    """
    stack = []
    for name_path in tokens:
        if len(name_path) == 2:
            name, path = name_path
            stack.append(name)
            for s_name in stack:
                assert any(s_name.endswith(e) for e in endings), (s_name, endings)
                assert path.startswith(base_path), path
                yield s_name, path
            stack = []
        elif len(name_path) == 1:
            stack.append(name_path[0])
        else:
            assert False, name_path