Removing characters before form_validation

[eluser]pistolPete[/eluser]
[quote author="jeffpeck" date="1257213543"]My understanding is that the callback function is only intended to return true or false. If you return $str modified that would always evaluate to true. You need to also edit the POST input. Right?[/quote]

No, read the user guide: http://ellislab.com/codeigniter/user-gui...#callbacks

You can also process the form data that is passed to your callback and return it. If your callback returns anything other than a boolean TRUE/FALSE it is assumed that the data is your newly processed form data.