Input message field attribute data

Nonliteral input message fields can be defined to allow for attribute data, extended attribute data, or both.

When defined to do so, MFS initializes to blanks and reserves the first bytes of the message field for attribute or extended attribute data. These first bytes are filled in by a field edit routine or in its preparation of an output message. When attribute or extended attribute space is specified, the specified field length must include space for the attribute or extended attribute bytes.

Sometimes input messages are updated by an application program and returned to the device. The application program can simplify message definitions if the message uses attribute data as the output message, and the attribute data bytes are defined in the input message, also.

When a field edit routine is used, it can be designed (as the IMS-supplied field edit routine is) to set attribute bytes on fields in error. In this way, erroneous fields can be highlighted before the segment edit routine returns the message to the device. In this case, the application program is not concerned with attribute bytes.