The Rules syntax MVC was implemented in https://gitlab.com/gitlab-org/gitlab/issues/27863, which introduced a new syntax for defining rules that allow you to provide an array of matching criteria (first match wins) to which a behavior is tied. Rules is more flexible and will ultimate replace the rigid structure of the existing `only/except` logic (implemented in issues under epic https://gitlab.com/groups/gitlab-org/-/epics/1237)