title: custom regex in route requirements
body: <p>I'm trying to make a route parameter match an alphanumeric value that's 3 to 15 characters long. Code looks like this:</p>
  
  <pre><code>TestBundle_new:
  pattern:  /message/new/{name}
  defaults: { _controller: TestBundle:Message:new }
  requirements:
      name:  [a-zA-Z0-9]{2,15}
  </code></pre>
  
  <p>Unfortunately routing.yml fails to load. I was wondering if there is anything I can do to make this work?</p>