Sure, if we make that assumption then we can make lots of
"simplifications" to XML to make it harder to type and easier to
generate. Then it can be as popular to end users as TeX, PDF or
PostScript instead of as popular as HTML.
Personally, I am not willing to make that assumption and I'm glad that
the ERB did not. SGML would be just another forgotten technology if it
had made that assumptions.
Once we reject that assumption, the restriction on MDC is reasonable.
Paul Prescod