title: Invalid regular expression error
body: <p><br/>
  I'm trying to retrieve the category part this string "<code>property_id=516&amp;category=featured-properties</code>", so the result should be "featured-properties", and I came up with a regular expression and tested it on this website <a href="http://gskinner.com/RegExr/" rel="nofollow">http://gskinner.com/RegExr/</a>, and it worked as expected, but when I added the regular expression to my javascript code, I had a "Invalid regular expression" error, can anyone tell me what is messing up this code?</p>
  
  <p>Thanks!</p>
  
  <pre><code>var url = "property_id=516&amp;category=featured-properties"
  var urlRE = url.match('(?&lt;=(category=))[a-z-]+');
  alert(urlRE[0]);
  </code></pre>