title: Future Proofing Changes to Validation of Username/Password Field in ZFCUser
body: <p>I've been looking around at how to change the actual validation process of the registration fields in the ZFCUser module in Zend Framework 2.</p>
  
  <p>There is a lot about extending and adding new fields etc. to the form but not validating these fields or extending the existing validation.</p>
  
  <p>I have taken a look inside the code and found the RegistrationForm.php file and added my customer Regular Expression filters.</p>
  
  <p>This works well and as expected but I am worried about this being over-written on any future upgrade.</p>
  
  <p>How would I go about doing this so it is upgrade safe? Is it a case of extending a specific class or adding it as a local file in my custom modules as I have done with the view files.</p>