Validating a Tag

Hello,

I am using the acts_as_taggable_on plugin (which derivates from
acts_as_taggable_on_steroids). My question is: How can I validate that
my tags doesn’t have any special characters such as . / \ etc. It
seems this validations are not included in the plugin. Can you give me
any guide in which is the best way to make this validations?

Thanks again,

Elías

Anyone can point me in a direction?