What it does is to encourage people to use ordinary-looking field names
for poorly designed fields which don't have the benefit of public review.
this sounds like a variant of the cliche about security through obscurity.
that's a lousy analogy. we're not talking about security here, we're
essentially talking about a social convention.
nobody is pretending that this convention prevents people from deploying
code that generates or accepts poorly-designed message headers. we're
only discussing whether the X- convention is useful.
Keith