title: Number after dollar sign in regex
body: <p>I have found out a code below </p>
  
  <pre><code>&lt;?php $string = 'April 15, 2003'; 
  $pattern = '/(\w+) (\d+), (\d+)/i'; 
  $replacement = '${1}1,$3';
  </code></pre>
  
  <p>I just want to know why this 1 after ${1} is declaired and why the value 3 is assigned before the end of the string symbol ?</p>