...
TBD: is OVC truly needed here, or is this a result of the SDE above for elements that have no way to get a value at unparse time - but the element turns out to be unused at unparse time.
Array Variables and dfdl:newVariableInstance
In many cases dfdl:newVariableInstance is not sufficient because what are needed are array variables.
.e., when parsing element i+1 you have to refer to a "variable" defined as part of element i.
You can't do that with dfdl:newVariableInstance because of the scope it has. If you introduce a dfdl:newVariableInstance for an array element, it's scope will be that element only. If you introduce it outside the array element there will be only one instance for the whole array.
But you can do an "array variable" with a hidden element. (Doesn't have to be hidden, but that's the sensible way to use it.)
The headache being the relative path to it., and then the fact that the most natural thing to do is to put both IVC and OVC on it (though the OVC may not be needed in many cases).