Atom 1.0

<published>

When an entry first appeared, as distinct from when it last changed. Only updated is required, which is why so many Atom feeds carry no publication date.

RSS has one date per item and Atom has two: <published> for first appearance and <updated> for the most recent meaningful edit. Only <updated> is required, which is why so many Atom feeds carry no publication date at all.

Keeping both is what lets a reader sort by publication while still detecting edits. Setting <published> to the build time defeats the entire distinction.

Format: Atom 1.0
Namespace: Atom Syndication Format 1.0
Parent: <entry>
How many: At most one per <entry>.

What it contains

Nothing — this element holds a value rather than other elements. Its content is text, and the constraints below are what that text has to be.

Cardinality and constraints

At most one per <entry>.

RFC 3339, exactly as <updated>.
Should not change once the entry has been published.
Optional — unlike <updated>, which is required.

What our validator does

Not checked: only <updated> is required, so the date pattern is applied there. A malformed <published> passes.

We do not catch this one

That is an RSS date in an Atom feed: RFC 822 where RFC 3339 is required. Our checks apply the pattern to <updated> only, so this one passes — and readers that parse it strictly will simply have no publication date for the entry.

Broken and fixed

Both documents below are well-formed XML — that is the point of this corpus — and both are run through the validator on every test run. The verdicts here are what it returned, not what we expect it to.

broken

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <id>urn:uuid:60a76c80-d399-11d9-b93c-0003939e0af6</id>
  <title>Example</title>
  <updated>2026-08-10T09:00:00Z</updated>
  <author><name>Ada Lovelace</name></author>
  <entry>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <title>Hen lays egg</title>
    <updated>2026-08-10T09:00:00Z</updated>
    <published>Mon, 10 Aug 2026 09:00:00 GMT</published>
  </entry>
</feed>

No issue reported. This defect passes our checks.

fixed

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <id>urn:uuid:60a76c80-d399-11d9-b93c-0003939e0af6</id>
  <title>Example</title>
  <updated>2026-08-10T09:00:00Z</updated>
  <author><name>Ada Lovelace</name></author>
  <entry>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <title>Hen lays egg</title>
    <updated>2026-08-10T09:00:00Z</updated>
    <published>2026-08-09T18:30:00Z</published>
  </entry>
</feed>

No errors. Warnings may remain — a conforming feed can still be missing a self link — but nothing here is wrong.

Where it reaches

Related elements

All 49 elements

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