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Subject: Conref range: Is constraint on last member of range necessary oruseful?

I'm writing up my explanation of conref range for my book and in explaining
the rule that the first and last elements of the range must be the same type
but intermediate members need not not be, it occurs to me that there's
really no point in having the constraint on the last member of the range.

Since I obviously didn't think about this too much at the time the mechanism
was proposed, I'm wondering if there was more thinking behind the constraint
than is evident from the language of the spec itself.

My questioning of the value of the constraint comes from this analysis:

1. The requirement that the referencing and referenced elements have
compatible parent elements ensures that the start element of the range is
valid in the referencing context.

2. It is possible to define sequence content models that allow a given type
to occur in multiple places within the sequence but that allows different
following siblings. This means that the referencing element could refer to a
range that is inconsistent with the sequence rules in the referencing
context. Since this case is not explicitly disallowed, it must not be a
concern. This means that strict DTD validity of the conref result cannot be
ensured in the general case and there is no general requirement to ensure

Likewise, since there are not constraints on the intermediate members beyond
common parentage, there must be no general concern about DTD validity of the
resolved result.

3. Given (2) it can't possibly help to require the last member of a sequence
to be the same as the start since it cannot make the result more valid.

4. Requiring that the start and end of the range be the same disallows use
of conref range for referencing sequences where the content model does not
allow the initial type to occur at the end of the range.

For example, say you have a specialized topic type that defines a set of
distinct specializations of <section> and puts them in a specific order. It
would be impossible to use conref range to re-use the sequence of sections
from another topic of the same type even though the result must be DTD

Thus, the requirement seems to be both unnecessary (it doesn't help ensure
correctness or sensibility of the conref result) and it disallows legitimate

Perhaps for 1.3 we should consider removing this constraint.



Eliot Kimber
Senior Solutions Architect
"Bringing Strategy, Content, and Technology Together"
Main: 512.554.9368

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