title: Regex for a string up to 20 chars long with a comma
body: <p>I need to define a regex for a string with the following requirements:</p>
  
  <ul>
  <li>Maximum 20 characters</li>
  <li>Must be in the form <code>Name,Surname</code></li>
  <li>No numbers and special characters allowed (again, it's a name&amp;surname)</li>
  </ul>
  
  <p>I already tried something like <code>^[^1-9\?\*\.\?\$\^\_]{1,20}[,][^1-9\?\*\.\?\$\^\_\-]{1,20}$</code> but as you can find, it also matches a 40 chars long string.</p>
  
  <p>How can I check for the whole string's maximum length and at the same time impose 1 comma inside of it and obviously not at the borders?</p>
  
  <p>Thank you</p>