Sets up a record stream consisting of segments from a segmented
    string field. Because a single segmented string field value is
    made up of multiple segments, a record stream that includes
    a segmented string field is nested. The outer loop retrieves
    records that include the segmented string field and the inner
    loop retrieves the segments from this field, one at a time.
    Therefore, a FOR statement that retrieves segmented strings must
    be nested within a START_STREAM or FOR statement.