title: Javascript RegExp issue
body: <p>I have a Regular Expression: <code>[a-z]{</code>
  which is a valid expression as per <code>Javascript's</code> <code>RegExp</code>.</p>
  
  <p>But if i change it to: <code>[a-z](</code>
  It's not a valid expression. I need to escape <code>"("</code> to make it work.</p>
  
  <p>Why does the <code>"{"</code> without escaping works?
  Is there a way to force Javascript to return it as invalid expression?</p>