title: Validate a form field against multiple constraints
body: <p>I have built a registration form where I want to validate fields in it.
  In my <code>RegistrationFormType</code> I have following code:</p>
  
  <pre><code>public function getDefaultOptions(array $options)
      {
          $collectionConstraint = new Collection(array(
              'email' =&gt; new Collection(array(
                  new NotBlank(),
                  new Email(array('message' =&gt; 'Invalid email addressadsfa')),
                  )),
              'username' =&gt; new Email(array('message' =&gt; 'arg Invalid email addressadsfa')),
              'code' =&gt; new MaxLength(array('limit'=&gt;20)),
              'plainPassword' =&gt; new MaxLength(array('limit'=&gt;20)),
          ));
  
          return array(
              'csrf_protection' =&gt; false,
              'validation_constraint' =&gt; $collectionConstraint,
          );
      }
  </code></pre>
  
  <p>Problem is: The email validation does not work. What am I doing wrong?</p>