def _append_summary_to_markdown(*, markdown: str, summary: str) -> str:
    """
    Append a interface summary string to a specified markdown string.

    Parameters
    ----------
    markdown : str
        Target markdown string.
    summary : str
        Target summary string.

    Returns
    -------
    markdown : str
        Result markdown string.
    """
    if summary == '':
        return markdown
    if markdown != '':
        markdown += '\n\n'
    markdown += f'**[Interface summary]** {summary}<hr>'
    return markdown