Abstract
Instead of referencing RFC 3339 for Date Constructs, reference XML Schema Part 2.
Status
New proposal.
Rationale
Atom is an XML vocabulary and off-the-shelf XML tools are much more likely to have libraries that easily and directly support xsd:dateTime than RFC 3339 date-times.
Proposal
Change 3.3 to read:
A Date construct is an element whose content MUST conform to the dateTime type defined in [W3C.xmlschema-2]. In addition, Date constructs MUST contain time zone information and match the following regular expression: [0-9]{8}T[0-9]{2}:[0-9]{2}:[0-9]{2}(\.[0-9]+)?(Z|[\+\-][0-9]{2}:[0-9]{2})
Add a new reference:
[W3C.xmlschema-2] Byron, P. and Malhotra, A, "XML Schema Part 2: Datatypes Second Edition", W3C xmlschema-2, October 2004
Impacts
Only the details of validating Date Constructs.
Notes
To avoid the problem of dates without timezones, which has been the source of some discomfiture, we could add the constraint that a Date Construct must also match this regular expression:
[0-9]{8}T[0-9]{2}:[0-9]{2}:[0-9]{2}(\.[0-9]+)?(Z|[\+\-][0-9]{2}:[0-9]{2})
how is this different from above?
Although personally, I have some reservation about using pattern facets on non-string types.
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Let's take credit for all five requirements: the regular expression specified above, ISO 8601, RFC 3339, xsd:dateTime, and w3cdtf.
I don't know of any valid tool produced dates which would not conform to all four, so the requirement on the producer side should not be onerous.
This would enable the widest range of readers.