"comment">//   mp:    is a reference to the whole multi_pass instance</span>
        <span class="comment">//   t:     is the character/token to test for validity</span>
        <span class="comment">// </span>
        <span class="comment">// This method is expected to return true if the parameter t </span>
        <span class="comment">// represents a valid character/token.</span>
        <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span cla