[RFC3339] defines a syntax for timestamps to represent date and time in the Internet. The present document defines an extension syntax that achieves the following properties:

• The extension suffix is completely optional, making existing [RFC3339] timestamps compatible with this format.

• The format is compatible with the pre-existing popular syntax for attaching time zone names to timestamps [JAVAZDT].

• The format provides a generalized way to attach additional information to the timestamp.

We refer to this format as the Internet Extended Date/Time Format (IXDTF).

This document does not address extensions to the format where the semantic result is no longer a fixed timestamp that is referenced to a (past or future) UTC time. For instance, it does not address:

• future time given as a local time in some specified time zone, where changes to the definition of that time zone (such as a political decision to enact or rescind daylight saving time) affect the instant in time represented by the timestamp;

• "floating time", i.e., a local time without information describing the UTC offset or time zone in which it should be interpreted; or

• the use of timescales different from UTC, such as International Atomic Time (TAI).

However, additional information augmenting a fixed timestamp may be sufficient to detect an inconsistency between the intention and the actual information in the timestamp, such as between the UTC offset and time zone name. For instance, inconsistencies might arise because of:

• political decisions, as discussed above,

• updates to time zone definitions being applied at different times by timestamp producers and receivers, or

• errors in programs producing and consuming timestamps.

While the information available in an IXDTF string is not generally sufficient to resolve an inconsistency, it may be used to initiate some out-of-band processing to obtain sufficient information for such a resolution.

In order to address some of the requirements implied here, related specifications in the future might define syntax and semantics of strings similar to those described in [RFC3339]. Note that the extension syntax defined in the present document is designed in such a way that it can be useful for such specifications as well.