Due to how control names and client ids are allocated inside during an Ajax request, it is difficult to
to connect input data and field validation errors to the fields, since the control name and client id are different
during the processing of the submitted form data and during the subsequent render. Starting in 5.4, the
key used to identify a field inside the org.apache.tapestry5.ValidationTracker is this new validation id,
which is assigned on first read.
If a field inplements {@link org.apache.tapestry5.Field} but not Field2, then the control name is used as the
validation id (which will work correctly during non-Ajax requests).
This assumes a "flat" field structure, where a given component renders only once (not multiple times, inside
a {@link org.apache.tapestry5.corelib.components.Loop}.