A MAP statement defines alternate groups of fields in a union. During execution, one map at a time is associated with a shared storage location. When you reference a field in a map, the fields in any previous map become undefined, and are succeeded by the fields in the map of the newly referenced field. Also:
A UNION declaration can appear only within a STRUCTURE declaration.
The amount of memory used by a union is that of its biggest map.
Within a UNION declaration, the order of the MAP statements is not relevant.
The UNION line is part of an inherently multiline group of statements, and neither the UNION line nor the END UNION line has any special indication of continuation. You do not put a nonblank in column six, nor an & in column one.
Each field-declaration in a map declaration can be one of the following:
Declaration of a typed data field