associative terminals generates an error.  This is useful for
comparison operations.  For example, if the input string is 
<tt>6 == 7 == 8 == 9</tt>, the parser should generate an error.  If '=='
is declared as <tt>nonassoc</tt> then an error will be generated. </p><p>

All terminals not used in the precedence/associativity declarations are
treated as lowest precedence.  If a shift/reduce error results,
involving two such terminals, it cannot be resolved, as the above
conflicts are, so it will be reported.<