ABOUT THE CODE
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WHAT HAPPENS WHEN A TEMPLATE EDITOR IS OPENED FOR A RESOURCE

The template editor uses a dedicated class for each field type (or family of field types).
These classes are all subclasses of the common base class NuTemplateElement. For things like
lists, there is a subclass NuTemplateGroupElement from which you can instead subclass to
have some of the work done for you.

When opening a resource, the template editor first creates a NuTemplateStream for the template
resource and calls readOneObject: on it until it runs out of data, instantiating a hierarchy
of NuTemplateElement subclasses for based on the template.

After that, it creates a NuTemplateStream for the resource and loops over the template object
hierarchy, creating a copy of each item, and then calling readDataFrom:containingArray: on
the copy, which in turn reads data from the NuTemplateStream and stores it in its instance
variables. For this to work, subclasses of NuTemplateElement *must* implement the NSCopying
protocol.

This results in an object hierarchy that describes the entire resource using template fields
containing the data, which can now be edited, displayed in lists, etc.


WHAT HAPPENS WHEN THE TEMPLATE EDITOR IS CLOSED

As soon as the template editor is closed, another NuTemplateStream is created for the
resource and passed to all template fields (the copies with the resource data, not the
pre-parsed template hierarchy), via writeDataTo:, which is where they should write their
data to the stream. Before that, sizeOnDisk is called on each NuTemplateElement to
calculate the new size of the resource before the actual process of writing them out.
This size must include the size of all of their sub-items, and writeDataTo: must call
these sub items if they are to be written to disk.


SPECIAL CASE: LISTS