Mark Pilgrim: History of RSS date formats.
Go read Mark’s points regarding RSS 2 and the use of the Dublin Core elements to get some context for what follows. If you’re really new to RSS and the issues around it, Mark has another page with the goods.
As a developer, I totally agree that ISO 8601 is easier to parse. It’s just a better way to represent a timestamp for computers to read. That’s a technical reason for using the Dublin Core date element, but not a terribly compelling reason to abandon native RSS 2 elements. And, honestly, “either way works, but we like doing it this way” is not a compelling reason either.
I don’t think that
<pubDate>
should be omitted in preference to the Dublin Core counterpart. Why? Because like it or not, as things are,
<pubDate>
is the defined tag for expressing publication date in the RSS 2.0 spec.
Having said that, I fully realize that
<pubDate>
is defined as an optional element. And the use of externally defined elements via namespace is allowed. But, I think it’s odd to rely upon external elements that offer identical functionality (albeit in a different form) as the declared specification.
A Developer’s Perspective
Let’s consider the task of RSS 2 implementation from a developer’s perspective.
If I were to write a new RSS parser (and believe me, I am not that stupid), I would first and foremost take the specification for RSS 2 and implement that to the letter. Every element that is defined there would be supported, regardless of whether it were optional or not. (Maybe it’s just me, but as a developer, the spec is the Bible. It has to be followed or things don’t work.)
If I were to stop right there without support for any of the existing namespaces, my parser would work, but it would be poor indeed. It should be complete by implementing the RSS 2 spec alone (for RSS 2 feeds that is). But a growing number of RSS 2 feeds today rely on the Dublin Core namespace to express common tags defined by the RSS 2 spec, so my parser would ignore those elements since it just implements the RSS 2 spec. For example, with the new RSS 2 template for Movable Type, any feeds it produces would be missing dates and category assignment in the eyes of my RSS 2 reader. Pretty significant, considering the date is the when of blogging.
I think Dave’s concern about all this is that the specification of RSS 2 is weakened by using alternative formats to replace elements it already defines. Let’s take this to the extreme: where every single element of RSS 2 is replaced by externally defined elements. Silly, right? And destructive to the goal of RSS — using the acronym Dave acknowledges: “Really Simple Syndication”.
The Publisher’s Perspective
Let’s look at this from the other angle. If I were completely new to RSS and wanted to implement a feed for my site, I would first and foremost take the specification for RSS 2 and implement that to the letter. I would use
<pubDate>
since dc:date isn’t part of the specification and not having any information on the optional namespace extensions, I would be ignorant of it.
Having followed the specification, I would have an expectation that anyone using a RSS 2 reader should have no problem processing my RSS 2 feed fully. Dates and all. But if there are some readers that don’t process
<pubDate>
and expect Dublin Core date tags instead, that would be a little frustrating to me.
Common elements like date and category should be part of the basic elements defined by RSS 2. And they are. And the publisher should look no further than the simple spec that Dave provides.
So What Then?
<pubDate>
should be used as the preferred date tag for RSS 2 feeds. If you want to use ISO 8601 dates, feel free — but
<pubDate>
tags should also be present for the benefit of all RSS 2 readers (whether they provide support for the Dublin Core extension or not).
Here’s another interesting tidbit. RSS 2 defines both
<pubDate>
and
<lastBuildDate>
elements. Some are using the Dublin Core to replace
<pubDate>
— but that tag looks like this:
<dc:date>2003-06-21T10:00:00-05:00</dc:date>
. This tag doesn’t describe what it applies to — one might wonder if it is meant as the publication date or the last build date or maybe it defines the author’s birthday? Who knows? The RSS 2 spec doesn’t define what the Dublin Core “date” tag is used for. The Dublin Core spec doesn’t define what the “date” tag means in the context of an RSS 2.0 document. So one can only infer. Hardly a specification.
And no, I’m not taking Dave’s side just because he linked to me yesterday.
Can we all agree that no one is legitimately going to e-mail a “.pif” file as an attachment to anyone? Every mail server/client in the world should be deleting these things automatically, upon arrival.
If you read my 
