> And I have to say than Bison is not BNF.

I understand that, but BNF is a general term referring to an
*abstract* (meta)syntax and every textbook presents it with slightly
different syntactic conventions.

I use BNF regularly, but never using the specific syntax your
mode supports.  Hence my question:

>> In what kind of circumstances would this be used?

E.g. what have you used it for?


        Stefan