fier">Fields</span><span class="special">&gt;</span>
    <span class="identifier">BodyWriter</span><span class="special">(</span><span class="identifier">header</span><span class="special">&lt;</span><span class="identifier">isRequest</span><span class="special">,</span> <span class="identifier">Fields</span><span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">h</span><span class="special">,</span> <span class="identifier">value_type