Atom 1.0

<published>

When an entry first appeared, as distinct from when it last changed — the element RSS has no equivalent for.

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 34 elements

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