title: How specify parameter's format in Nelmio ApiDocBundle
body: <p>I use <code>input</code> property of <code>@ApiDoc</code> annotation for specifieng of parameters of my api that are form's fields.</p>
  
  <pre><code> * @ApiDoc(
   *      section="User",
   *      resource=true,
   *      input={
   *          "class"="Nik\UserBundle\Form\UserType",
   *      },
   *     ....
  </code></pre>
  
  <p><code>data_class</code> of form is a entity that have constraint validation for properties.</p>
  
  <p>I expect that nelmio api doc specify parameter format as validation constraints of entity, but format are empty.</p>
  
  <p><a href="https://i.stack.imgur.com/zxuQZ.png" rel="noreferrer"><img src="https://i.stack.imgur.com/zxuQZ.png" alt="enter image description here"></a></p>
  
  <p>How can i specify parameter formats in nelmio ApiDocBundle?</p>
  
  <hr>
  
  <p><strong>EDIT</strong>:
  maybe i write a bad question.</p>
  
  <p>we can specify parsers for <code>input</code> &amp; <code>output</code>, if we no specify parser for these, it call all parser for <code>input</code> &amp; <code>output</code>, then all parser are called for <code>UserType</code>.</p>
  
  <p><code>nelmio</code> have a parser named <a href="https://github.com/nelmio/NelmioApiDocBundle/blob/master/Parser/ValidationParser.php" rel="noreferrer">ValidationParser</a> that have a method named <a href="https://github.com/nelmio/NelmioApiDocBundle/blob/master/Parser/ValidationParser.php#L183" rel="noreferrer">parseConstraint</a> that set <code>format</code> for input &amp; output, but this method is not called for my document, why?</p>