UI.WidgetValueSource

This is similar to the hashref passed into TT2's ->process() method
In most cases the source for widget values is the Request.
But expressly does NOT have to be the request... it can be any subclass of WidgetValueSource (and since Collection::Attributes subclasses WidgetValueSource, almost every object in BOP can be used as a source)
vs_simple_form() and Table() are specific cases that don't use the Request for the source