Regex for slot validation in Rasa x UI

Hi, I have app_id which is 8 or 9 digit numerical number. I created intent ‘app_id’ and entity and slots ‘e_app_id’ which will be used later in custom actions. But i want app_id to be validated before passing to

  • How to validate slot e_app_id using regex in rasa-x.
  • what would be regex for 8 or 9 digit code
  • how to link regex with slot for validation?
  • I could not find any documentation for this