The format keyword isn’t used in this way very often.
It allow you to create a logical over one file but use the formating of another file.
File1 contains fields FLDA, FLDB, FLDC and FLDD
File2contains fields FLDA, FLDB, FLDC
Logical1 is created over file1 and would contain the four fields
Logical2 is created over file1 but with format FIle2 it would deliver the data from File1 but just the three
fields of file2.