Saašha Metsärantala <[log in to unmask]>:
> As far as I remember, intervals including seasons were excluded because of the difficulties to validate them - or the impossibility to validate many of them.
> (...) But the answer is not obvious with 1980-21/1980-23, 1980-23/1980-21
The former period is valid, the latter is invalid. Everything else would go against the spirit of ISO 8601.
Well, arguably all the proposed extensions to the MM field are abominations, because stuff like 1980-21/1980-12-30 would be a valid period although 21 is larger than 12.
> 1980-07/1980-21 or 1980-07/1980-23.
These, indeed, depend on the exact definition of "season", which the DIS was lacking but the FDIS might have (I dunno).