The field description specifications for an externally described file can be used to rename a field within a record for a program or to specify control level, field indicator, and match field functions. The field definitions (attributes) are retrieved from the externally described file and cannot be changed by the program. If the attributes of a field are not valid to an RPG IV program the field cannot be used. Diagnostic checking is done on fields contained in an external record format in the same way as for source statements.
Normally, externally described input fields are only read during input operations if the field is actually used elsewhere in the program. If DEBUG or DEBUG(*YES) is specified, all externally described input fields will be read even if they are not used in the program.