In the long run we need to find a way to support multiple widget libraries (e.g. some forms might want a keyboard-friendly 3-field date input rather than the jquery-ui datepicker).
As a quick workaround (because I want to do this in a Mirebalais form) I want to support
to signify that we just want the hidden input with the date value, and no visible datepicker.
Eventually this syntax should allow us to have other widgets.