DateTimeZ definition missing

[ottonomy]

Several properties of AchievementCredential (see AchievementCredential) for example like validFrom declare that the expected data type is DateTimeZ (I presume this is an ISO 8601 DateTime with the Z time zone identifier for UTC?), but this data type is missing from the table linked when you click DateTimeZ in the AchievementCredential table.

Can we add that definition?