I 'd have one short question: 
To prevent the possibility of endless loops, in SGML exist the open
entity.
But I haven 't found something like that in the XML Working Draft. So,
is it possible to construct endless loops in XML?
--Horst
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Horst Silberhorn 
FORWISS  Am Weichselgarten 7  D-91058 Erlangen 
Email: silberh@forwiss.uni-erlangen.de
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