4.7.1 Direct element constructors
Normalization rules make use of italicized variables called
ElementContent.  By convention, an italicized variable is 
supposed to refer to a BNF nonterminal in some grammar, but 
there is not such nonterminal.  
I realize that you wish to have a single rule that summarizes
the multiple kinds of element content, but you should not assume
that creating an italicized ElementContent constitutes a 
formal definition.

I haven't checked, but I suspect
that some of the other italicized variables in this section,
such as AttributeList, are not BNF nonterminals either.

This comment also applies to section 8.1.5 "Extension", where
we also find the undefined AttributeAll.