title: what is X-Cascade header
body: <p><a href="http://rack.rubyforge.org/doc/" rel="noreferrer">Rack documentation</a> says that</p>
  
  <pre><code>File servers support X-Cascade header
  </code></pre>
  
  <p><a href="https://github.com/josh/rack-mount" rel="noreferrer">rack-mount</a> says that</p>
  
  <pre><code>Rack::Mount supports Rack’s +X-Cascade+ convention
  </code></pre>
  
  <p>What is  X-Cascade ? I could not find any documentation on  X-Cascade.</p>