@stof The point is not to make it extendable for multiple packages, but on a special case basis. Of course if you are building a reusable bundle you would want to roll out your own `TypeGuesser`, however there are special cases where for one specific projects in that one specific case, you might want to add a new supported button type, or maybe disable the support for `submit`.

Both are totally valid points. However I do not think we must be overly restrictive in this case. There are still valid use-cases for having a `protected` function here.