The current whattf/v.nu schema for HTML5 is non-conformant with the spec in that it includes some (obsoleted) elements that the spec does not define at all.

i recognize that that the schema by itself is already not completely conformant with the spec, in that the schema does not (and cannot) completely express all of the constraints that are defined in the spec. But  I think there is a signficant difference between the case of being incomplete in terms of conformance, and the case of having specific instances of non-conformance (such as this case of allowing elements that the spec doesn't define).

I also well recognize that the fact that those element are in the schema is a conscious design choice, as well as the fact that it's not an issue for v.nu because v.nu doesn't use the schema in isolation but instead uses it along with the additional assertions-processing step -- where those elements get explicitly reported as obsolete.

And I recognize the value of having v.nu explicitly catch and report those particular elements, and I'm not suggesting that behavior should change (if anything, I think v.nu should do such reporting for even more elements, and even obsoleted attributes, too.)

But I think that people -- regardless of what we try to do to limit availability of the schema and to admonish people to not use it alone for validation -- will eventually end up using the schema in "standalone" fashion, outside of v.nu, without using the assertions processing or any of the other non-schema checking that v.nu does. So there's some potential confusion/harm in having a non-conformant schema around at all.

I'm not sure what the original rationale was for having the elements in the schema to begin with, but if it was due to wanting to have the obsolete-element errors reported first -- instead of having it first report the (really unhelpful) jing default "Error: Element foo not allowed as child of element bar in this context" that it would otherwise report if the elements were not in the schema -- then I think one way to deal with that would be to switch the order of processing in v.nu such that the assertions checking is run prior to the schema checking.