title: HTML attributes without quotation marks?
body: <p>I've always thought html requires quotation marks in his properties:</p>
  
  <p><code>&lt;div class="service_definition"&gt;</code> or <code>&lt;div class='service_definition'&gt;</code></p>
  
  <p>But recently i noticed that the w3 validator doesn't recognize the following as an error:</p>
  
  <p><code>&lt;div class=service_definition&gt;</code></p>
  
  <p>So is it all right if i omit the quotation marks? Or are there any restrictions?</p>