> (b) make sure your processor distinguishes between elements
> with [validity]=invalid and those with [validity]=notKnown
> (again, how you do this is between you and your processor,
> and out of scope for the XSD spec); and
You might like to note that Saxon's schema processor, and perhaps some other
products, expose this distinction by allowing you to select "strict" or
"lax" validation. Strict validation fails if the outcome is
[validity]=notKnown, whereas lax validation succeeds.