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Michael Brennan wrote:
> Certainly, though, there are valid
> use cases for some applications' need to augment a document's infoset. But
> why do certain augmentations (e.g. attribute and element defaulting) deserve
> special status, and why must they be conflated with the task of validation?
> There are plenty of strategies the application could employ to do infoset
> augmentation that do not require that core XML standards conflate the roles
> of validation and value defaulting in such a manner that every consumer of
> XML documents *must* assume that it *may* not be able to reliably interpret
> the content of a document without validating it, and cannot assume that the
> mere task of validation may alter the infoset.
(I have nothing to add, but this paragraph is worth repeating.)
When designing a markup vocabulary, it's often convenient
to specify default values in the schema itself. However,
the inconvenience to applications which are then forced to run
a validator outweighs this when validation is expensive.
Schema notations for validation should be as powerful as necessary;
schema notations for augmentation should be as simple as possible.
I believe as a consequence that we need more than one notation.