::</span><span class="identifier">value_at_c</span></code></a> and <a class="link" href="../sequence/intrinsic/metafunctions/value_at_key.html" title="value_at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at_key</span></code></a>) of the <span class="emphasis"><em>N</em></span>th
        element is <code class="literal">attribute_type<span class="emphasis"><em>N</em></span></code> with const-qualifier
        and ref