[tei-council] permit <hi> in <formula>?

[Lou Burnard]

At present <formula> has a content model which permits only text or 
model.graphicLike.

It would be convenient to expand this to include model.hiLike since 
formulae often include things like "superscript x" for values of x for 
which no character exists in Unicode (and there quite a few of them). 
<hi rend="superscript">x</hi> though verbose is a bit easier to remember 
than &#xABCD; for most values of ABCD

This lead me also to look at  the other elements which are meant to be 
just plain text eg the various xName elements used in the gaiji module; 
our chums ident idno code etc: here's the current state of play for 
those addicted to consistency to consider...

The current state is that for most of them rng:text is the only
permitted content. Maybe that should generally be macro.xText, and
maybe macro.xText should include <hi> ?

charName : rng:text
code  : rng:text
eg : rng:text
egXML : rng:text | macro.anyXML
formula : text | model.graphicLike
g : rng:text
gi : rng:text
glyphName : rng:text
idno : macro.xtext
ident : rng:text
localName : rng:text
pc  :  rng:text | model.gLike | c
unicodeName : rng:text