def METHOD_NAME(root_dir):
    """raise error if this program cannot continue, based on the inputs"""
    if not os.path.exists(root_dir):
        raise RuntimeError("Cannot find " + root_dir)
    if not os.path.isdir(root_dir):
        raise RuntimeError("Not a directory: " + root_dir)
    if not is_definitions_directory(root_dir):
        msg = "Not a NeXus definitions root directory " + root_dir
        raise RuntimeError(msg)