I see that the W3C XML Security Working Group has updated the Working Draft of their non-normative XML Security schemas in RELAX NG Compact Syntax.
RELAX NG's creator Murata-san made a comment on the schemas on the DSDL-comment mailing list:
An interesting thing about these RNG schemas is the use @Algorithm
attribute for controlling contents, which represent parameters of the specified
algorithm. The original XSD schemas did not capture this co-constraint.
Hopefully XSD 1.1 now has the capability to use attribute values to select types, so the XSD schemas may end up being upgraded too. I don't know the WG's plans on this. XSD 1.1 caught up with RELAX NG in a couple of areas related to power, but at such a cost in carbuncular complexity that one wonders why anyone would bother.XSD has a bad track record of partial implementations (despite some excellent complete ones) that people are still well advised to stick with using XSD features they know are supported by the actual systems they will use: you have to reverse engineer from the products the feature set from the standard you will use. RELAX NG simply does not have this problem, which should be an issue of interest for security, I would have thought.