Since posting this I did something even more useful. :-) I went back
to ISO 8879 in which, of course, the use of paremeter entity
references is allowed in both the "internal" and "external" subsets.
As a programmer I reckon that the different handling of parameter
entities between the internal and external subsets makes things MORE
complicated rather than simpler.
I knew there was something wrong with the avowed claim that XML was a
subset of SGML. If they're to be allowed (and they are allowed in
some odd places in XML) then let them occur wherever SGML lets them
occur.
Regards, Trevor.
--"Real Men don't Read Instruction Manuals" Tim Allen, Home Improvement