title: What does "deceptive request routing" mean in the new HTTP spec (RFC 7231)?
body: <p>In <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.1" rel="noreferrer">RFC 2616</a>, the 400 response code was for syntax errors.</p>
  
  <blockquote>
    <p>The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.</p>
  </blockquote>
  
  <p><a href="https://httpwg.github.io/specs/rfc7231.html#status.4xx" rel="noreferrer">RFC 7231</a> broadens the applicability of 400. The spec gives a few other examples of client errors, but I'm not sure what they mean.</p>
  
  <blockquote>
    <p>The 400 (Bad Request) status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).</p>
  </blockquote>
  
  <p>In particular, what would constitute "deceptive request routing"?</p>