an> parser components have well defined attribute
        types. Grammars and rules are no exception. But since both need to be generic
        enough to be usable for any parser their attribute type has to be explicitly
        specified. In the example above the <code class="computeroutput"><span class="identifier">roman</span></code>
        grammar and the rule <code class="computeroutput"><span class="identifier">first</span></code>
        both have an <code class="computeroutput"><span class="keyword