Syntax: bf(%start) tt(nonterminal symbol)

    By default b() uses the the LHS of the first rule in a grammar
specification file as the start symbol. I.e., the parser tries to recognize
that nonterminal when parsing input. 

    This default behavior may be overriden using the tt(%start) directive.
    The nonterminal symbol specifies a LHS that may be defined anywhere in
the rules section of the grammar specification file. This LHS becomes the
grammar's start symbol.



