A keyword followed by a host language variable. A request handle
    points to the location of a compiled Oracle Rdb request. If you
    do not supply a request handle explicitly, Oracle Rdb associates a
    default request handle with the compiled request. Your must use
    a request handle when you want to make an identical query to two
    different databases.

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

    You can put parentheses around the host language variable name.