This class is used for all dates in originInfo.
This class uses a structured copied from form_model_gui_binding.xml in samples provided with the forms block in Cocoon 2.1.10. The idea is that the elements within a subject element (topic, geographic, etc.) are handled by a single class "subject-widgets-class", which uses a union/case/group structure to deal with the different types. The local-name of the element is bound to the "type" widget, and the union uses the type to determine which group to implement. So, a mods_topic element causes type="mods_topic", which causes the >group id="mods_topic"< to be instanced.
Note: this class uses "xidentifier" as its id instead of "identifier", because the latter appears to be a reserved word in Cocoon Forms and breaks the form.