xss_clean in CI 3

You should've read the upgrade instructions or at least searched the forum topics to see if the question hasn't already been answered here (it was, multiple times).

xss_clean is no longer part of form validation. The alternative is not to use it, as xss_clean is doing sanitization and not validation.

xss_clean is part of security helper. If you need to do it, after validation you do a:

$this->load->helper('security');
$value = $this->input->post('formvalue', TRUE); // ...where TRUE enables the xss filtering

... i think...

Also, you can enable global xss filtering in the config.php file:

$config['global_xss_filtering'] = TRUE;

Please don't recommend 'global_xss_filtering'. That is a bad solution, even worse than manually applying xss_clean on individual inputs.