Tracks information related to user input validations. This information is:
- The input values provided by the user.
- Any validation exceptions associated with input fields.
The tracker must differentiate between components (which will implement the
Field interfaces) and fields. It is a one to many relationship, because each field may be called upon
to render itself multiple times within a request, because of
Loop or other similar
components.
Internally, the tracker indexes its information in terms of the
Field.getElementName for each rendering of the component (the mechanics of Tapestry ensures that this is unique within
the form).
Validation trackers must be serializable, as they will almost always be stored into the
HttpSession.
Trackers are used by only a single form within a single page; they are not threadsafe.
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