I think most people will have the expectation that `on-click` will work similar to the native `click` attribute where you'd use the `show(1,2,3)` syntax. Formatters I think you can get away with the other syntax because it's sort of understood there's going to be some magic happening when it comes to calling those functions, where as events are something where surprises like that are going to be more confusing. Plus it might cause people to assume that you can do things like  `on-click="show:1,2,3 | anotherFunc:1,2,3"`.