The validation code here is overriding the validation code specified by
userforms, which means that standard validation (e.g. of required fields) isn’t
working. It also means that validation that is being applied (e.g. to email
fields) is producing new error messages (instead of replacing the old error
message) every time the field is validated (every key press, on blur event etc.)
This is causing more harm than good, and should be removed.

There is a PR in the works with the jQuery Validation plugin (see
https://github.com/jzaefferer/jquery-validation/issues/966) which will mean we
can re-introduce parts of this code without further breaking accessibility.