def _match_suffix(suffix, ffilter):
    """Return file type (textual description) for a given suffix.

    Parameters
    ----------
    suffix : str
        File extension to check (must include the leading dot).
    ffilter : dict
        ffilter : dict
        Known file types. The keys contain descriptions (names), whereas the
        values contain the corresponding file extension(s).

    Returns
    -------
    ftype : str | None
        File type (None if unknown file type).
    """
    for ftype, ext in ffilter.items():
        if suffix in ext:
            return ftype