title: Check if string has valid Twig syntax
body: <p>Simple, in a Symfony2 app, inside a function of a service class, I want to check if a given string passed as argument has valid Twig syntax... </p>
  
  <pre><code>public function checkIfValidTwig($twigString)
  {
      $isValid = false;
      $isValid = someWay-&gt;toCheckIf()-&gt;itIsValid($twigString);
      return $isValid;
  }
  </code></pre>
  
  <p>Any idea?</p>