AS/400 Record I/O questions

I'm not an AS/400 type, although I have written several C programs for it 
due to a requirement to provide cross-platform compatibility.  I have some 
questions regarding record I/O processing (non-IFS files).

1. How is support for variable records provided or enforced?  For example, 
suppose you specify "type=record, recfm=vb, lrecl=84, blksize=172" as part 
of the fopen() attribute for a file. 
        a. In the case of output, are you suppose to provide a record 
descriptor word of 4-bytes (e.g. LLbb) at the beginning of the record that 
describes the length of the RDW and data           portion of the record? 
In MVS, this is a requirement. 
        b. In the case of input, are you provided with an RDW preceding 
the data portion of the record?
        c. If a record is written that actually exceeds 84 bytes, does 
fwrite() care (e.g. returns a value of 0)?
        d, Does fwrite() check if the record size is a multiple of 
blksize?

2.  I haven't tried using variable length records, but I have tried doing 
record I/O using fixed length records.  For example, I specified 
"type=record,recfm=f,lrecl=80" as part of the fopen()
     attribute.
        a.  In the case of output, fopen() did not complain if I wrote a 
record that exceeded 80 bytes.  And, in the case of input, I specified 
"lrecl=100", which did not match the lrecl that I 
             used to write the data (e.g. lrecl=80), and fread() didn't 
complain.  I just got 100 bytes.  Is it fair to assume that the I/O system 
does not enforce/check the fopen() attributes with
            respect to the file?  In MVS, the file's attributes are stored 
on disk with the file, and they are strictly enforced and checked.

TIA