The "date" and "datetime" fields now use the corresponding HTML5 input types

wtforms.fields.DateField and wtforms.fields.DateTimeField now use the HTML5 date and datetime input types instead of the generic "text" field. 

I'm not sure if this is the preferred way vs widget = widgets.Input('date'), but this seems reasonable since the html5 input types are defined anyway, in case additional functionality gets added to the widget in the future.

This allows browsers (desktop and mobile) to render whatever date/datetime selectors that they implement (if any).