title: Required or not depending on one field - Embedded forms Symfony2
body: <p>I'm doing a Forum bundle where you can add (or not) a vote to your subject.
  The problem is that the embedded form (the question and the answers) has to be required only if a boolean is true.</p>
  
  <p>I first tried some solutions I found here and there on the internet but nothing worked.
  Then I created 2 forms, one with a vote, another without and I created a little switch with some JQuery.</p>
  
  <p>The problem is that when I want to create a subject and only fill one form, HTML5 tells me there are fields required I didn't fill in the other form, it doesn't only send the form I'm trying to submit, it apparently submits both.</p>
  
  <p>Do you know why and how I could solve this, or maybe a simpler technique to dynamically define if a field is required or not ?</p>
  
  <p>Thanks in advance !</p>