questions about element declarations

The proposals on the table seem to me to raise several questions about
element declarations which we haven't yet discussed here:

* Should XML retain SGML's prohibition on multiple declarations for the
same element (11.2.1)?

*  Should XML restrict the use of #PCDATA to content models of the form
(#PCDATA), or of the form (#PCDATA | A | B | ...)*, as a way of avoiding
the mixed-content trap (11.2.4) and/or of simplifying RE handling

* Should XML prohibit the use of inclusion and exclusion exceptions in
element declarations? (11.2.4, 11.2.5)?

* Should XML prohibit content-model references to undeclared elements

* Should XML forbid use of the '&' connector in content models

* Should XML allow nondeterministic content models (