pre>
</div>


<p>
It should be noted that as of H2O version 1.7.0, there are limitations when compared to ordinary web application server with support for Rack such as Unicorn:
<ul>
<li>no libraries provided as part of Rack is available (only the interface is compatible)
</ul>
</p>

<p>
In addition to the Rack interface specification, H2O recognizes status code <code>399</code> which can be used to delegate request to the next handler.
The feature can be used to implement access control and response header 