Corrected a comment in forms/forms.py; refs #16612.

    def changed_data(self):

        if self._changed_data is None:

            self._changed_data = []

            # XXX: For now we're asking the individual widgets whether or not the

            # XXX: For now we're asking the individual fields whether or not the

            # data has changed. It would probably be more efficient to hash the

            # initial data, store it in a hidden field, and compare a hash of the

            # submitted data, but we'd need a way to easily get the string value