Yes, that's a plausible scenario in which a defaulted ID attribute
might be useful. Sorry... XML rules it out.
As for my having defaulted the "target" attribute in the annotated
spec, the "target" is the *same* on every annotation, that's why
it's defaulted. Nothing could be more different from an ID attribute.
The annotation doesn't say (maybe should) that the thing that
generates the HTML copies through any attributes it doesn't
recognize, so the defaulted target="spec" ends up in every one
of the hundreds of annotations. -Tim