title: Regexp (?<=string) is giving invalid group error?
body: <p>I'm trying to create a regular expression to match a string like <code>&lt;tag&gt;something&lt;/tag&gt;</code> and I want the result to return only <code>something</code> without the tags.</p>
  
  <p>i tried using:</p>
  
  <pre><code>string.match(/(?&lt;=&lt;tag&gt;).*?(?=&lt;\/tag&gt;)/g);
  </code></pre>
  
  <p>but its giving an error: </p>
  
  <p><code>SyntaxError:Invalid regular expression: /(?&lt;=&lt;tag&gt;).*?(?=&lt;\/tag&gt;)/: Invalid group</code>;</p>
  
  <p>why is it not working?</p>