Hey thanks for pointing this out. Every time this gets posted to HN someone notices something else.

The format you spotted in the Venn diagram was:

    2023-09-01T10:12:07.284307

This is indeed only valid under ISO 8601 since RFC 3339 always requires a timezone.

So the Venn diagram wasn't wrong, but I agree it was misleading.

I've now updated the diagram to add the following format, which is valid under both standards:

    2023-09-01T02:12:07.284307Z