title: Validate February as part of date validation using regexp
body: <p>I am trying to validate a date using regexp (it's for homework on regexp - yes I know there are better ways doing this in Java using the API)</p>
  
  <p>So far I managed the following expression:</p>
  
  <pre><code>(0[1-9]|[12][0-9]|3[01])/(0[1-9]|1[012])/((18|19|20|21)\\d\\d)
  </code></pre>
  
  <p>I would like to add a check for February, i.e. cannot have 30 and 31 in the days is 2 is in the month 
  (let's assume no leap year check)</p>
  
  <p>How can I add this check into my expression?</p>