title: How do you change the default format to XML in Symfony?
body: <p>I'm writing a restful XML API for a university assignment, the spec requires no HTML frontend.</p>
  
  <p>There doesn't seem to be any documentation (or guessable functionality) regarding how to change the default format? Whilst thus far I have created all templates as <code>...Success.xml.php</code> it would be easier to just use the regular ones and set this globally; I really expected this functionality to be configurable from YAML.. yet I have found some hard coded references to the HTML format.</p>
  
  <p>The main issue I'm encountering is that part of the assessment is returning a 404 in a certain way (not as a 404 :/), but importantly it must always return XML, and the default setup of a missing route is a HTML 404 not XML (so it only works when I use <code>forward404</code> from an action running via a XML route.</p>
  
  <p>So in summary, is there a way to do this / what class(es) do I have to override?</p>