Allowing custom characters in validation

[eluser]KeyStroke[/eluser]
Hi,

I'm trying to use the form_validation library to validate some fields in my application. The problem is the fields need to allow a custom set of characters. For example: the username field should only allow alpha characters, numbers, underscores and dots.

How is this done?

Appreciate your help.

[eluser]GSV Sleeper Service[/eluser]
if none of the preset rules match, you'll have to make a custom callback function.
manual