James Clark on Validation
I believe that the right kind of validation can make interoperability over time more robust than the alternative, simpler approach of having an implementation just ignore anything that it doesn’t need.
This is mostly in response to Mark Baker’s Validation Considered Harmful post; I wonder what James would have to say about Dave Orchard’s work on versioning, especially his XML Schema thoughts (and, to a lesser degree, his theory of compatible versions).