Utility method to check that all extensions in the provided set are valid

    :param extensions:
    :param allow_multifile:
    :return:

def check_extensions(extensions: Set[str], allow_multifile: bool = False):
    """
    Utility method to check that all extensions in the provided set are valid

    :param extensions:
    :param allow_multifile:
    :return:
    """
    check_var(extensions, var_types=set, var_name='extensions')

    # -- check them one by one
    for ext in extensions:
        check_extension(ext, allow_multifile=allow_multifile)