title: Form labels translation key with parameters
body: <p>I have a form in symfony2 where I add a checkbox for let's say "Terms and Conditions" that needs to be checked. I want to add a link to "Terms and Conditions" label which I want to pass it as a parameter, let's say %url% like this</p>
  
  <blockquote>
    <p>messages.en.yml</p>
  </blockquote>
  
  <pre><code>site.terms: Hiermit akzeptiere ich die &lt;a href="%url%"&gt;AGB&lt;/a&gt;
  </code></pre>
  
  <blockquote>
    <p>In the Form type I have something like this</p>
  </blockquote>
  
  <pre><code>$builder
  ...
  -&gt;add('terms', 'checkbox', [
      'constraints' =&gt; [
          new True()
      ],
      'label' =&gt; 'site.terms'
  ]);
  </code></pre>
  
  <p>So the question is how can I add that url parameter or even an array of parameters to the form label.</p>
  
  <p>For avoiding escaping the HTML inside the form label I have overwritten the block label like this:</p>
  
  <pre><code>{% block form_label %}
      {% if not compound %}
          {% set label_attr = label_attr|merge({'for': id}) %}
      {% endif %}
      {% if required %}
          {% set label_attr = label_attr|merge({'class': (label_attr.class|default('') ~ ' required')|trim}) %}
      {% endif %}
      {% if label is empty %}
          {% set label = name|humanize %}
      {% endif %}
  
      {# added raw to avoid HTML Escaping #}
      &lt;label{% for attrname, attrvalue in label_attr %} {{ attrname }}="{{ attrvalue }}"{% endfor %}&gt;{{ label|trans({}, translation_domain)|raw }}&lt;/label&gt;
  {% endblock form_label %}
  </code></pre>