FREDI defaults the data element 0020 value to the incremental
count number of interchanges in the document. The number is
padded with zeros to satisfy minimum length requirement of the data
element.
When the interchange is created, the data element 0020 is assigned
the same value in the interchange header (UNB) and the interchange
trailer (UNZ).
When verifying syntactical correctness, an error is generated if
the value of this data element 0020 is not the same in the UNB and
UNZ.
When acknowledging a subject interchange, the 0020 in the UCI
segment contains the same value as that of the subject interchange.