 class="parameter">txn</span> is non-null, then the operation is
            performed using that transaction. In this event, large sections of
            the tree may be locked during the course of the transaction.
            </p>
        <p>
            If <span class="parameter">txn</span> is null, but the operation occurs in a
            transactional database, the operation will be implicitly transaction
            protected using multiple transactions. These transactions will be
            period