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<h2>Goal</h2>

Provides an object model for HTML form fields.  Fields are aggregated into tab definitions
using the {@link TabWithFields} {@link Tab} subclass.  Modeling & aggregating form fields this
way makes it easy to a) move fields between tabs by making changes in a single place and b) avoid
boilerplate HTML in the tabs' views.

The base interface is {@link InputField}.

<h2>Design</h2>
<p>
    InputFields are divided into categories.  The implementation of aggregation (see
    {@link R