title: Codeigniter use form validation for variable
body: <p>I've read somewhere that is possible to use Codeigniter's Form Validation also for my own variables and not only for form's inputs.</p>
  
  <p>For example I'd like to validate a url to say if it is valid but not retrieving it using POST or GET from a form.</p>
  
  <p>Do you know how or have a link?</p>