A common form requirement is to force the user to enter a
date so that it is greater than another. The attached form demonstrates
how to apply this requirement either at the data layer (using an XForms
constraint bind) or at the presentation layer (using the format option).
The XForms approach is preferable since it flags the data node as invalid
and would prohibit an XForms submission if an invalid date was provided.
Furthermore, an XForms bind is extremely powerful in that a single bind
can apply a constraint on a large set of nodes.