I'm new to this list. I discovered the EDTF draft while researching extensions to ISO 8601 that would
be appropriate for genealogical source data (much of which can be uncertain), so I was very happy to
find your work here!
As an exercise to get my arms around it, I'm writing a reference implementation in C# for Levels 0, 1,
and portions of level 2 (which will be open source).
I realize it is a work in progress, but I would like to suggest that the valid characters for season
qualifier be limited further than just non-whitespace. The current definition theoretically includes ",",
"/", "]", and "}", which creates a potentially ambiguous situation for parsers.
For simplicity in my own implementation, I'm using the "\w" regular expression character class as
implemented under C#/.NET, which includes all Unicode letters and numbers and a few punctuation
symbols including underscores.