pan>
    <span class="special">{</span>
        <span class="comment">// Build a std::vector from the subject's attribute. Note</span>
        <span class="comment">// that build_std_vector may return unused_type if the</span>
        <span class="comment">// subject's attribute is an unused_type.</span>
        <span class="keyword">typedef</span> <span class="keyword">typename</span>
            <span class="identifier">traits</span><span class="special">::</span><span class="identifier">build_std_vector<