The README says that wrapper: { class: false } should attach no classes to the wrapper. There were no tests for this case. I added tests, and they pass, except for check boxes.

To fix, I propose that wrapper: { class: false } should be interpreted as: "remove any classes that are not strictly necessary to make Bootstrap work correctly." Currently, that means removing mb-3 from wrappers, leaving no classes on most input types, but retaining the form-check that's needed to make check boxes and radio buttons work.

Would address some of #638 comments, and somewhat related to #738 -- but probably not a solution to the latter issue.