We stumbled upon them, sort of, with Drupal. Consider the using the visitor pattern for access where each visitor needs to return a value. (Drupal is old so yes

We stumbled upon them, sort of, with Drupal. Consider the using the visitor pattern for access where each visitor needs to return a value. (Drupal is old so yes return values is what you had) You may want to allow access, deny access or tell the system you have no opinion at all.