title: Use regular expressions to validate passwords
body: <p>I have a password field which should match the following conditions</p>
  
  <ol>
  <li>should have at least one letter and one digit</li>
  <li>should have minimum length of 5 and maximum length of 20</li>
  </ol>
  
  <p>Also, I would like to know if regular expressions are the same for all languages?</p>
  
  <p>Links to good tutorials to get started with Regular Expressions (assuming I have just a basic understanding) would also be nice.</p>
  
  <p>Thank you</p>