title: ?: Notation in Regular Expression
body: <p>for one of my classes I have to describe the following regular expression:</p>
  
  <pre><code>\b4[0-9]{12}(?:[0-9]{3})\b
  </code></pre>
  
  <p>I understand that it selects a number that: begins with 4, is followed by 12 digits (each between 0-9), and is followed by another 3 digits.</p>
  
  <p>What I don't understand is the the question mark with the semicolon (?:....). I've tried looking online to find out what this means but the links I've found were somewhat confusing; I was hoping someone could give me a quick basic idea of what the question mark does in this example.</p>