title: capturing group in regex
body: <p>I am exploring capturing groups in Regex and I am getting confused about lack of documentation on it. For ex, can anyone tell me difference between two regex:</p>
  
  <pre><code>/(?:madhur)?/
  </code></pre>
  
  <p>and</p>
  
  <pre><code>/(madhur)?/
  </code></pre>
  
  <p>As per me, ? in second suggests matching <code>madhur</code> zero or once in the string.</p>
  
  <p>How is the first different from second ?</p>