Conal Tuohy wrote:
> <date>
>         <date when="1640" cert="low"/>
>         <date notBefore="1620" cert="medium"/>
>         <date notAfter="1660" cert="high"/>
> </date>

This seems an elegant and flexible approach to me. It allows refinements 
like this, too:

<date>
         <date when="1640" cert="low"/>
         <date notBefore="1620" notAfter="1660" cert="medium"/>
</date>

where the certainty value applies to the whole date range. I would vote 
for this being incorporated into the guidelines as good practice.

Cheers,
Martin

-- 
Martin Holmes
University of Victoria Humanities Computing and Media Centre
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Half-Baked Software, Inc.
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