title: custom validations with acts-as-taggable-on
body: <p>Hi I am working on a Rails 3 project and I am using acts-as-taggable-on and everything works perfectly! :)</p>
  
  <p>I just have one question.</p>
  
  <p>Does anyone know how I can add my 'custom' validation to ActsAsTaggableOn::Tag? Any callbacks I can hook into (e.g before_tag_save)? or something similar?</p>
  
  <p>I need to run a regex on each 'tag' (to ensure that each tag does not contain any illegal characters) in my tag_list before I save my model and would like to know if there is a standard way of doing it.</p>
  
  <p>The way I solved the problem is by adding a validation method in my PostController which just iterates over the list of Tags and runs the regex, but this seems ugly to me.</p>
  
  <p>Any suggestions?</p>
  
  <p>Thank you in advance! :)</p>