RE: [xml-dev] XML Schema: nillable vs. minOccurs

1) Using nillable elements allows you to maintain full structure of the
markup in the instance document, even when meaningful content is missing. It
also, perhaps, gives the receiver a little extra insurance that nothing got
'lost' in the generation/translation of a document. Not an ironclad
guarantee, though...

2) Nil (or null) can be taken to mean 'undefined', rather than 'does not
exist'; although it's doubtful many applications will care about such fine
distinctions.