title: Perl question mark followed by colon pattern matching
body: <p>I have following perl pattern matching condition </p>
  
  <pre><code>(?:\s+\w+){2}
  </code></pre>
  
  <p>When it's applied on a Linux directory listing </p>
  
  <pre><code>-rw-rw-r-- 1 root root       36547 2011-03-18 18:41 abc.txt
  </code></pre>
  
  <p>It matches <code>root root</code></p>
  
  <p>What is <code>?:</code> doing in this?</p>