ition class,
            the definition of a couple of token types. Some of the token types do
            not expose a special token value (<code class="computeroutput"><span class="identifier">if_</span></code>,
            <code class="computeroutput"><span class="identifier">else_</span></code>, and <code class="computeroutput"><span class="identifier">while_</span></code>). Their token value will always
            hold the iterator range of the matched input sequence. The token definitions
           