I think Wendell's analysis has been interesting, thought-provoking,
and generally "spot on". One added thought:
> The investments you've already made in learning something, vs. the
> investments you're willing to make in learning something else
> (including the opportunity costs of doing so) -- those concerns are
> never far away.
One reason I like RELAX NG is that the investment needed to learn it,
while still too high to make it worth the effort in some cases, is
less than the investment needed to learn the equivalent
functionality of the DTD language or W3C XML Schema language.