A keyword followed by a host language variable. A transaction
    handle identifies each instance of a transaction. If you do not
    declare the transaction handle explicitly, Oracle Rdb attaches an
    internal identifier to the transaction.

    If you specify a transaction handle on a START_TRANSACTION
    statement, you must also specify the transaction handle on any
    COMMIT, FOR, ROLLBACK, START_STREAM, and STORE statements that
    relate to the transaction.

    You can specify this clause only once within a single START_
    TRANSACTION statement.

    In Callable RDO, use !VAL as a marker for host language
    variables.

    Normally, you do not need to use this argument. The ability to
    declare a transaction handle is provided for compatibility with
    other database products and future releases of Oracle Rdb.

    Do not use this argument in interactive RDO.