title: WSGI: what's the purpose of start_response function
body: <p>Could you supply a real-life example of <a href="http://wsgi.readthedocs.org/en/latest/" rel="noreferrer">WSGI</a> <a href="http://webpython.codepoint.net/wsgi_application_interface" rel="noreferrer"><code>start_response</code></a> function? (Web-server provides that function to wsgi application)</p>
  
  <p>I can't understand the <strong>purpose</strong> of introducing the <code>start_response</code>.</p>
  
  <p>(I've read like 10 identical texts about the WSGI standard. They all say "WSGI standard is..." None of them says "WSGI is designed this way <strong>in order to</strong>..." :()</p>