YYYY-MM-DDZ and THH.MM.SS. are (probably) not valid ISO8601 #18
Description
YYYY-MM-DDZ was allowed in the first version of the HAPI JSON schema. It seems that this is allowed in XML dateTime 1; 2. However, Pandas and other libraries do not accept it.
The justification for the regex that allowsTHH.MM.SS. (or THH.MM.SS.Z) is unknown, and some ISO 8601 parsers allow it 3, but although not explicitly stated, based on the ISO8601 documentation, it seems invalid.
For version 4 of HAPI, I recommend that we disallow YYYY-MM-DDZ and THH.MM.SS after checking to see if any servers use it.