title: Regex for number check below a value
body: <p>I'm still a beginner at regex so this is a little above me currently.</p>
  
  <p>I need to validate a number input to two characters and it can't be more than the value 12.</p>
  
  <p>The two numbers easy: </p>
  
  <pre><code>/^\d{1,2}$/
  </code></pre>
  
  <p>Then check that if there are two numbers then the first must be either 0 or 1, and the second must be either 0, 1, or 2.
  That part I don't know how to express, regularly...</p>
  
  <p>And also if possible I would like to have it in single regex statement.</p>
  
  <p>Any help appreciated. </p>