">boost</span><span class="special">::</span><span class="identifier">ignore_unused</span><span class="special">(</span><span class="identifier">kind</span><span class="special">,</span> <span class="identifier">payload</span><span class="special">);</span>
    <span class="special">});</span>
</pre>
<p>
        When a control callback is registered, it will be invoked for all pings,
        pongs, and close frames received through either synchronous read functions
        or asynchronous read functions. Th