The WWP encodes date ranges using the value= attribute of <date>, with the mechanism provided by ISO 8601. We do not use the TEI <dateRange> element. The ISO 8601 mechanism allows the expression of a period of time as:
a) start and end dates
b) duration of time
c) start date and duration
d) end date and duration
Method (a) is the simplest to use for discussion here, as the start and end date are simply expressed as described above, and juxtapositioned with a slash between them. For example:
I enjoyed tremendously the TEI10 conference at Brown 1997-11-14/1997-11-16. (Note that this could be abbreviated 1997-11-14/16.)
The TEI has its own mechanism for expressing a period of time, with the <dateRange> element, but the WWP does not use this method. Thus, the Guidelines have the example:
The Eddic poems are preserved in a unique manuscript (Codex Regius 2365) from <dateRange from="1250" to="1300"> the second half of the thirteenth century</dateRange>, ... (p 162)
However, since ISO 8601 can be used as the standard form for the value= attribute of date, and it can express a range on its own, the same passage could be encoded:
The Eddic poems are preserved in a unique manuscript (Codex Regius 2365) from <date value="1250/1300">the second half of the thirteenth century</date>, ...
The second method is the only method we use for encoding ranges of dates; in fact, <dateRange> is not in the WWP DTD.