def __getitem__(n):
    """Return n-th history record.

        Records are ordered by age, from latest (index 0) to oldest.

        Each record is a dictonary with at least the following items:

            tid -- transaction ID (a byte string, usually 8 bytes)
            time -- transaction timestamp (Unix time_t value)
            user_name -- name of the user responsible for the change
            description -- short description (often a URL)

        """
