Later… Quentin points out that:
The [ !supportEmptyParas] stuff is not standard HTML – it’s a proprietary Microsoft extension which used to have a nasty habit of turning up where it wasn’t wanted. Outlook would hide it, but some other non-MS programs wouldn’t. All of which makes me suspect that this wasn’t how the cake was meant to turn out.
I did a quick Google search and found another document by way of an example.