fsdb: where to learn something about it?

[Alex Martelli]

How would I go about learning something about fsdb?  It seems to be a
heavily underdocumented command.  I know the manpage states that only
those who are already expert in fsdb should be using it, but that one
is clearly a joke, besides, the SEMANTICS are not all that hard, at
least with 'S5'-like, simplistic filesystems, it's the SYNTAX itself
that I find to be mysterious given the almost-empty documentation.

Is there a paper or tech report somewhere with some syntax details
and/or more examples than the few ones in the manpage?  Is there a
BNF syntax somewhere so I can figure out how to say, for example, 
'place a doubleword with value A into disk block B at offset C'?

Experimentation can always take place on a suitably mashed filesystem
on a floppy disk, but trying out all variations on #Dsomething=blah
to guess the syntax of the one that will work, if any, gets old fast!

Thanks in advance for any suggestions...
-- 
Alex Martelli - CAD.LAB s.p.a., v. Stalingrado 53, Bologna, Italia
Email: (work:) martelli at cadlab.sublink.org, (home:) alex at am.sublink.org
Phone: (work:) ++39 (51) 371099, (home:) ++39 (51) 250434; 
Fax: ++39 (51) 366964 (work only), Fidonet: 332/401.3 (home only).