> > * 21 = Spring - Northern Hemisphere
> > * 22 = Summer - Northern Hemisphere
> Making the value of a date dependent on geography is problematic
It is, but sometimes it is unavoidable.
> Someone else suggested that we don't need separate codes for seasons in the Northern and Southern Hemisphere.
Sometimes we can't anyway.
> The point is to concisely designate whatever someone designates as summer, etc., in particular context,
Sometimes you don't know the context. For example, if you have the information about something happened in "Spring 1847", but don't know where ... not even within which hemisphere: How could we express that? I consider that the best usecases for the use of seasons in EDTF are precisely when the season is known, but the hemisphere is not.
As far as I remember, that is also the reason why we decided (a few years ago) that EDTF-seasons are not sortable.