DR 09-0207: WML: Custom XML and Smart Tags

[MURATA Makoto (FAMILY Given)]

While reviewing this text (and trying to rewrite it), I find that I do
not quite understand the differences of the three forms.  

I believe I understand Smart tags and Custom XML Markup. They are
mechanisms for embedding foreign elements without using foreign tag
names.  Custom XML Markup allows validation, while smart tags don't.

But I do not quite understand  structured document tags.  In my
understanding, their semantics are standardized with the exception of
the "alias" attribute.  All other subelements and attributes of 
 structured document tags have standardized semantics.  Am I right?

Cheers,
Makoto