At the moment, the specification is ambiguous on which calendar is used for temporal conversion/writing [1]. Reading the java code it appears it is using Java's OffsetDateTime which conforms to ISO8601 [2]. ISO8601 appears to explicitly disallow the Julian calendar (but only says proleptic gregorian can be used by mutual consent [3]).
Therefore I'd propose: 1. We make the ISO8601 + proleptic Gregorian + Gregorian calendars explicit in the specification. 2. Mention in an implementation note, that data migrated from other systems or data written by older systems might follow the Julian calendar (e.g. it looks like Spark only transitioned in 3.0 [4]). * Does anybody know of metadata available for systems to make this determination? * Or a recommendation on how to handle these? Thoughts? Thanks, Micah [1] This is esoteric but a few systems use 0001-01-01 as a sentinel value for null so does have some wider applicability [2] https://docs.oracle.com/javase/8/docs/api/java/time/OffsetDateTime.html [3] https://en.wikipedia.org/wiki/ISO_8601#Dates [4] https://issues.apache.org/jira/browse/SPARK-26651
