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2024-05-13 ⇒

# The 'iffy' XML namespace

➣ This post was meaningfully revised at 2025-08-30 @ 06:50 PM EDT. The previous revision is here, diff here. (See update history.)
➣ This post is expected to evolve over time. You can subscribe to ongoing updates here.

I want to do a lot of things with RSS that require extensions of RSS (as the RSS spec foresees).

The URL `http://tech.interfluidity.com/xml/iffy/` will mark an XML namespace in which some of these extensions will be defined.

The conventional prefix associated with this namespace will be `iffy`.

The current version of this namespace is `v0.0.1-SNAPSHOT`.

(`-SNAPSHOT` signifies that the version preceding that suffix has not yet been finalized. Much more to come!)

## Table of Contents

- `iffy:all`
- `iffy:completeness`
- `iffy:curation`
- `iffy:diff`
- `iffy:hint-announce`
- `iffy:in-reply-to`
- `iffy:initial`
- `iffy:item-ref`
- `iffy:policy`
- `iffy:provenance`
- `iffy:recent`
- `iffy:restriction`
- `iffy:revision`
- `iffy:selection`
- `iffy:single`
- `iffy:synthetic`
- `iffy:type`
- `iffy:uid`
- `iffy:update`
- `iffy:update-history`

## Element — `iffy:all`

### When beneath `iffy:curation`

`iffy:all` is a curation type, a description of how the feed is curated relative to the body of work a subset of which it presents.

Curation type `iffy:all` signifies that the full, unabridged collection of work is represented by `item` elements in this feed.

#### Example:

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/">
      <channel>
        <title>tech — interfluidity</title>
        <atom:link type="application/rss+xml" rel="self" href="https://tech.interfluidity.com/feed/index.rss"/>
        <iffy:curation>
          <iffy:all/>
        </iffy:curation>
        <!-- Other channel elements -->
        <item>
          <!-- Other item elements -->
        </item>
      </channel>
    </rss>

## Element — `iffy:completeness`

### Solely a channel level element

Contains one of the following four values:

1. `Ping`
2. `Metadata`
3. `Content`
4. `Media`

`iffy:completeness` describes the completeness that clients should expect of RSS `item` elements.

- `Ping` makes the least commitment. Items need not include a `guid` element, or any elements at all beyond RSS' requirement that at least one of `title` or `description` be present. RSS documents have completion `Ping` by default. Any or all items may meet the requirement for a higher completeness level, but no promises or commitment is made beyond the base specification.

- `Metadata` commits that each item MUST include a `guid` element, as well as meeting the base requirements for an RSS `item`.

- `Content` commits that each item, either inside its `description` tag, or via an extension such as `content:encoded`, includes the full content of the items it includes, suitable for independent rendering by any client capable also of resolving references to linked media externally. No limitation is placed on whether the full content is placed in a `description` element, in `content:encoded`, or in some other extension.

- `Media` augments `Content` by embedding attachments to subsidiary media inside the RSS document. Subsidiary media does not include all potential links, just links which share a prefix with the current RSS document, which by default means all links subsidiary to the parent of the RSS document as specified in an `atom:link`

  More information on this soon when `iffy:attachment` is defined

The four values represent nested, hierarchical levels of commitment. `Ping` commits to nothing more than the spec requires. `Media` makes every commitment promised by the prior three levels, and an additional one.

If not specified, no commitment is made, the feed should be considered `Ping`.

#### Example:

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/">
      <channel>
        <title>tech — interfluidity</title>
        <atom:link type="application/rss+xml" rel="self" href="https://tech.interfluidity.com/feed/index.rss"/>
        <iffy:completeness>Content</iffy:completeness>
        <!-- Other channel elements -->
        <item>
          <!-- Other item elements -->
        </item>
      </channel>
    </rss>

## Element — `iffy:curation`

### Solely a `channel` level element

`iffy:curation` provides a description of how the feed is curated relative to the body of work a subset of which it presents. It MUST include as a sub-element a curation type. The following curation types are defined:

- `iffy:all`
- `iffy:selection`
- `iffy:single`

#### Example:

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/">
      <channel>
        <title>tech — interfluidity</title>
        <atom:link type="application/rss+xml" rel="self" href="https://tech.interfluidity.com/feed/index.rss"/>
        <iffy:curation>
          <iffy:selection>
            <iffy:recent since="2024-08-16T22:22:14.297722-04:00" last="10" operator="and"/>
          </iffy:selection>
        </iffy:curation>
        <!-- Other channel elements -->
        <item>
          <!-- Other item elements -->
        </item>
      </channel>
    </rss>

## Element — `iffy:diff`

### When a subelement of `iffy:update`

MUST contain a URL, URI, or IRI of a human-reviewable a diff of the current updated and the final minor revision of the update prior (or of the initially published post, if the current update is the first declared update).

#### Example:

    <iffy:diff>https://tech.interfluidity.com/xml/iffy/index-diff-394986cb8d9c57f567d324e691a44d50102101ce-to-13de0232319ceab2f830591c318089d18cbec78d.html</iffy:diff>

See also `iffy:update-history` example.

## Element — `iffy:hint-announce`

### When a subelement of `item`

Represents a hint to RSS consumers that "push" — announce, rebroadcast, or notify — items whether this item should be so pushed. Consumers are free to ignore this hint or make use of it as they wish.

MUST contain an `iffy:policy` element, whose values MUST BE one of

- `Always` — the item should always be notified
- `Never` — the item should never be notified
- `Piggyback` — the item should be notified as part of digests or other announcements of multiple items, but should not constitute its own announcement.

MAY contain an `iffy:restriction` element, which represents an application-specific restriction over the consumers to which it is addressed. No restrictions are placed on the content of the `iffy:restriction` element. Applications can define restrictions as they see fit.

An `iffy:hint-announce` element with NO `iffy:restriction` or an empty `iffy:restriction` tag should be interpreted as the intended default for ALL applications not addressed by an `iffy:hint-announce` with a more specific restriction.

Multiple `iffy:hint-announce` elements may be placed within a single `item`, provided that only one has an omitted or empty `iffy:restriction`, and all `iffy:hint-announce` elements containing an `iffy:restriction` contain a unique restriction. Each `iffy:restriction` SHOULD apply to nonoverlapping application-specific contexts. If that is not the case, how applications prioritize or respond to conflicting `iffy-hint-announce` elements whose restrictions both apply must be determined by the application.

#### Example:

    <iffy:hint-announce>
      <iffy:policy>Piggyback</iffy:policy>
    </iffy:hint-announce>

## Element — `iffy:in-reply-to`

### When a subelement of `item`

Marks an item as a reply to some other `item`, which may be published anywhere. Contains one `iffy:item-ref`.

#### Example:

    <iffy:in-reply-to>
      <iffy:item-ref href="https://tech.interfluidity.com/feed/index.rss" type="application/rss+xml" guid="https://tech.interfluidity.com/2024/11/12/supporting-single-item-rss/index.html" />
    </iffy:in-reply-to>

## Element — `iffy:initial`

In general, describes the initial state of the item referred to by the element that contains it.

MAY contain any or all of

- an `atom:title` element, containing the initial title of the item, which may have since been revised.
- an `atom:link` element, containing the initial link to the item, which may have since been revised.
- an `iffy:uid` element, containing the `guid` of the item that has been updated.
- an `atom:published` element containing the date-time of initial publication
- a sequence of `dc:creator` elements, describing the initial authorship of an item, which may since have been revised.

Note: We define an `iffy:uid` element, rather than rely upon `atom:id`, because `atom:id` requires that its contents be an IRI, but we mean to impose no such restriction.

### When a subelement of `item` > `iffy:update-history`

An `iffy:initial` MAY BE included under `item` > `iffy:update-history`, but is recommended ONLY IF the title, authorship, or link have changed.

Since `item` > `guid` and `item` > `pubDate` never change, generators SHOULD NOT include these items under `item` > `iffy:update-history`. They are available directly in the containing item.

#### Example:

    <iffy:initial>
      <!-- Perhaps more recent updates, and the current item, include more authors -->
      <dc:creator>First Author, Esq.</dc:creator>
    </iffy:initial>

### When a subelement of `item` > `iffy:synthetic` > `iffy:update` AND `iffy:type` of the synthetic element is `UpdateAnnouncement`

An `iffy:initial` MUST BE provided containing all of the analogous values defined in the `item` whose update the announcement describes.

This information would not be otherwise available, because values in the parent `item` describe the synthetic update announcement post, rather than the post whose update is announced.

- If an `item` > `title` is defined in the post that was updated, that MUST BE recorded as `atom:title`
- If an `item` > `link` is defined in the post that was updated, that MUST BE recorded as `atom:link`
- If an `item` > `guid` is defined in the post that was updated, that MUST BE recorded as `iffy:uid`
- If an `item` > `pubDate` is defined in the post that was updated, that MUST BE recorded as `atom:published`
- If an `item` > `dc:creator` is defined in the post that was updated, that MUST BE recorded as `dc:creator` If, in the post that was updated, authorship was defined using `item` > `author` or `item` > `atom:author` those items should be converted into a form appropriate for `dc:creator` elements.

#### Example:

    <item>
      <pubDate>Thu, 20 Jun 2024 13:10:00 -0400</pubDate>
      <guid isPermalink="true">
        https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index-updated-2024-06-20-13-10-00.html
      </guid>
      <link>https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index-updated-2024-06-20-13-10-00.html</link>
      <title>Updated: Feedletter tutorial</title>
      <!-- other item elements -->
      <iffy:synthetic>
        <iffy:type>UpdateAnnouncement</iffy:type>
        <iffy:update>
          <atom:updated>2024-06-20T17:10:00Z</atom:updated>
          <!-- other iffy:updated elements -->
          <iffy:initial>
            <atom:title><![CDATA[Feedletter tutorial]]></atom:title>
            <atom:link href="https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index.html"/>
            <iffy:uid>https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index.html</iffy:uid>
            <atom:published>2024-01-29T15:30:00Z</atom:published>
            <dc:creator><![CDATA[Steve Randy Waldman]]></dc:creator>
          </iffy:initial>
        </iffy:update>
      </iffy:synthetic>
      <dc:creator><![CDATA[Update-o-Bot]]></dc:creator>
    </item>

### When a subelement of `item` > `iffy:synthetic` > `iffy:update-history` AND `iffy:type` of the synthetic element is `UpdateCumulation`

An `iffy:initial` MUST BE provided containing all of the analogous values defined in the `item` whose update the announcement describes.

This information would not be otherwise available, because values in the parent `item` describe the synthetic update cumulation (summary) post, rather than the post whose update history is documented.

- If an `item` > `title` is defined in the post that was updated, that MUST BE recorded as `atom:title`
- If an `item` > `link` is defined in the post that was updated, that MUST BE recorded as `atom:link`
- If an `item` > `guid` is defined in the post that was updated, that MUST BE recorded as `iffy:uid`
- If an `item` > `pubDate` is defined in the post that was updated, that MUST BE recorded as `atom:published`
- If an `item` > `dc:creator` is defined in the post that was updated, that MUST BE recorded as `dc:creator` If, in the post that was updated, authorship was defined using `item` > `author` or `item` > `atom:author` those items should be converted into a form appropriate for `dc:creator` elements.

## Element — `iffy:item-ref`

Represents a reference to an RSS `item` in RSS data available elsewhere.

`iffy:item-ref` SHOULD be an empty XML element, given meaning by its attributes.

- An `iffy:item-ref` MUST contain an `href` attribute, which points to a source of RSS data or to an HTML document that refers to RSS data in an HTML `link` element.

- An `iffy:item-ref` SHOULD contain a `type` attribute. The type should either be `text/html` or `application/*rss+xml` where the `*` may refer to the empty string (so just `application/rss+xml`) or a prefix, like `application/x-single-item-rss+xml`. (If a type attribute is missing, a consumer MAY try to examine the contents at `href` and do the right thing.) (Mime types can, as always, include a parameter, like `text/html;charset=UTF-8`.)

- An `iffy:item-ref` MUST contain a `guid` attribute UNLESS the `href` refers to single-item RSS.

To resolve an `iffy:item-ref` consumers should:

1. Check the `type` attribute, or if missing, check the contents referred to by the `href`, to see whether the referent is an HTML or an RSS document.

2. If the referent is an RSS document and the `iffy:item-ref` includes a `guid` attribute, the `item-ref` refers to the RSS `item` element containing a `guid` element whose contents matched the `iffy:item-ref`'s `guid` attribute.

3. If the referent is an RSS document and the `iffy:item-ref` does NOT include a `guid` attribute, then the `item-ref` refers to the single RSS item in the document. If there is more than one RSS `item`, the resolution fails.

4. If the referent is an HTML document and the `iffy:item-ref` contains a `guid` attribute, the consumer must gather all HTML `link` elements with `rel="alternative"` and `type="application/*rss+xml` where the `*` may refer to the empty string (so just `application/rss+xml`) or a prefix, like `application/x-single-item-rss+xml`. The type may also contain a parameter, like `application/x-single-item-rss+xml;completeness=Content` The consumer tries `link` elements whose `type` attribute is an exact match to the `iffy:item-ref`'s `type` attribute first, in the order they appear in the HTML file, and then other `link` elements with `type="application/*rss+xml`, in the order they appear. For each `link` tried, if the linked RSS contains that an RSS `item` with the `item-ref`'s specified `guid`, then the `item-ref` refers to that `item` and the resolution process terminates immediately.

5. If the referent is an HTML document and the `iffy:item-ref` DOES NOT contain a `guid` attribute, the consumer must search for an HTML `link` element whose `rel="alternative"` and whose `type="application/x-single-item-rss+xml"`. If there are no or multiple `link` elements so specified, resoluton fails. If there is a unique `<link rel="alternative" type="application/x-single-item-rss+xml" href="...">`, and its referent contains RSS data with a single `item` attribute, the `iffy:item-ref` successfully resolves to that attribute.

#### Example (single-item RSS):

    <iffy:item-ref href="https://tech.interfluidity.com/2024/11/12/supporting-single-item-rss/index.rss" type="application/x-single-item-rss+xml" />

#### Example (RSS, by guid):

    <iffy:item-ref href="https://tech.interfluidity.com/feed/index.rss" type="application/rss+xml" guid="https://tech.interfluidity.com/2024/11/12/supporting-single-item-rss/index.html" />

#### Example (HTML, search for single-item RSS):

    <iffy:item-ref href="https://tech.interfluidity.com/2024/11/12/supporting-single-item-rss/index.html" type="text/html" />

#### Example (HTML, search all feeds for guid):

    <!-- here the item guid is also the permalink, that is the href. but that needn't always be the case! -->
    <iffy:item-ref href="https://tech.interfluidity.com/2024/11/12/supporting-single-item-rss/index.html" type="text/html" guid="https://tech.interfluidity.com/2024/11/12/supporting-single-item-rss/index.html" />

## Element — `iffy:policy`

In general, represents a statement of some kind of policy with respect to its containing element, suggested to feed consumers for handling a feed or item.

### When a subelement of `iffy:hint-announce`

Please see `iffy:hint-announce`.

## Element — `iffy:provenance`

In general, this element tracks the provenance of a feed or item. It can be at the `channel`-level or at the `item`-level. Also, `iffy:provenance` elements can be nested within `iffy:provenance` elements (see below).

### When no `shape` attribute is set, or `shape="sequence"`

`iffy:provenance` elements of shape `sequence` (the default) contain

- a sequence of one or more `atom:link` elements, each of whose
  - `rel` attribute is MUST BE `via`
  - `href` attribute MUST BE the URL of an RSS feed from which the base contents of this item were drawn
  - `type` attribute SHOULD BE `application/rss+xml`
- optionally, a terminating `iffy:provenance` whose shape attribute is set to `merge`

If the item or channel from which the current item or channel was sourced does not contain an `iffy:provenance`, then the current item should include just one `atom:link`.

If the item from which the current item was sourced does contains an `iffy:provenance`:

- If the contained `iffy:provenance` has no `shape` attribute set, or if `shape` is set to `sequence`, then the current feed SHOULD include all items of that element, with the URL of the feed from which the item was sourced PREPENDED as an `atom:link`. This will ensure the most immediate source will be the first `atom:link` element. The origin — or at least the source for which no further provenance is known — will be the last `atom:link` or `iffy:provenance` subelement.

- If the contained `iffy:provenance` has a `shape` attribute set to `merge`, then the full element should be included as a subelement, after an `atom:link` to its source.

If one is present, processors SHOULD use a channel level `atom:link` element with `rel="self"` and `type="application/rss+xml"` to as the basis for provenance in source documents. See RSS Best Practices. However, if no such `atom:link` is available at the `channel` level, processes may default to the URL by which they accessed the source.

#### Example (from here):

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:sy="http://purl.org/rss/1.0/modules/syndication/" xmlns:slash="http://purl.org/rss/1.0/modules/slash/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:wfw="http://wellformedweb.org/CommentAPI/" xmlns:content="http://purl.org/rss/1.0/modules/content/" xmlns:dc="http://purl.org/dc/elements/1.1/">
      <channel>
        <title>interfluidity, all blogs</title>
        <!-- Other channel elements -->
        <atom:link type="application/rss+xml" rel="self" href="https://www.interfluidity.com/unify-rss/all-blogs.rss"/>
        <item>
          <title>Industrial policy and ecosystems</title>
          <guid isPermalink="true">https://drafts.interfluidity.com/2024/05/11/industrial-policy-and-ecosystems/index.html</guid>
          <author>nospam@dev.null (Steve Randy Waldman)</author>
          <link>https://drafts.interfluidity.com/2024/05/11/industrial-policy-and-ecosystems/index.html</link>
          <!-- Other item elements -->
          <iffy:provenance>
            <atom:link type="application/rss+xml" rel="via" href="https://drafts.interfluidity.com/feed/index.rss"/>
          </iffy:provenance>
        </item>
      </channel>
    </rss>

### When the `shape` attribute is set to `merge`

`iffy:provenance` elements of shape `merge` describe an `item` or `channel` that has derived from multiple sources. When `shape="merge"`, the ordering of items within `iffy:provenance` is not significant.

Any `iffy:provenance` element of shape `merge` can contain any number of `atom:link` and `iffy:provenance` of shape `sequence`, or with no `shape` attribute set.

When merging items or feeds whose provenance is itself the result of a merge, processors SHOULD bring what would become elements of a nested `iffy:provenance` with `shape="merge"` into the top-level merge.

In other words, `iffy:provenance` elements with shape `merge` should not be directly nested, one inside the other. Elements of the inner `iffy:provenance` with `shape="merge"` should be flattened into the outer `iffy:provenance` with `shape="merge"`.

`iffy:provenance` elements with shape `merge` CAN and SHOULD be indirectly nested, when a merge brings in an `iffy:provenance` element of shape `sequence` (or no shape set), which then includes a nested `iffy:provenance` elements with shape `merge`.

## Element — `iffy:restriction`

In general, represents an expression of some kind of restriction over the application of its containing element.

### When a subelement of `iffy:hint-announce`

Please see `iffy:hint-announce`.

## Element — `iffy:recent`

### When beneath `iffy:selection`

`iffy:recent` describes a selection (see also `iffy:curation`) that represents the most recent posts to a feed.

(Curations that are selections of recent posts represent the most common use-case for RSS, although most feeds do not yet annotate themselves as such.)

`iffy:recent` has three attributes:

- `last` — When the attribute `last="<positive-integer-value-n>"` is defined, the feed displays a subset of the most recent `n` items, if there are at least `n` items in the unabridged body of work.

- `since` — When the attribute `since="<timestamp>"` is defined, all elements more recent than the given timestamp are represented as items in this feed. Timestamps may de defined as atom "date constructs" OR in the format expected for `pubDate` in standard RSS.

- `operation` — Values must be one of `and` or `or`. Determines whether, if both `last` and `since` are set, items must be more recent than the `since` timestamp AND among the most recent `n` defined by `last`, or whether all items more recent than the `since` timestamp OR among the most recent `n` defined by `last` are included. If no `operation` is set, and both `last` and `since` are set, then `operation` should be presumed to default to `and`.

#### Example:

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/">
      <channel>
        <title>tech — interfluidity</title>
        <atom:link type="application/rss+xml" rel="self" href="https://tech.interfluidity.com/feed/index.rss"/>
        <iffy:curation>
          <iffy:selection>
            <iffy:recent since="2024-08-16T22:22:14.297722-04:00" last="10" operator="and"/>
          <iffy:selection>
        </iffy:curation>
        <!-- Other channel elements -->
        <item>
          <!-- Other item elements -->
        </item>
      </channel>
    </rss>

## Element — `iffy:revision`

MUST contain a URL, URI, or IRI of a either a fixed past revision or the current (potentially evolving) revision of an item.

Example:

    <iffy:revision>https://tech.interfluidity.com/xml/iffy/index-oldcommit-13de0232319ceab2f830591c318089d18cbec78d.html</iffy:revision>

See `iffy:update-history` example.

## Element — `iffy:selection`

### When beneath `iffy:curation`

`iffy:selection` is a curation type, a description of how the feed is curated relative to the body of work a subset of which it presents.

Curation type `iffy:selection` signifies that this feed is the result of a potentially arbitrary query against or restriction of the full body of work.

An `iffy:selection` tag SHOULD contain subelements, documenting the query or restriction that produced this selection, ideally with sufficient information to reproduce the selection from a specified upstream source.

This specification defines only a single query type for `iffy:selection`:

- `iffy:recent`

However, many other queries or selections are possible, and at least for now, there are no restrictions on descriptions that might be provide. It is a playground for developer creativity.

#### Example (recent items):

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/">
      <channel>
        <title>tech — interfluidity</title>
        <atom:link type="application/rss+xml" rel="self" href="https://tech.interfluidity.com/feed/index.rss"/>
        <iffy:curation>
          <iffy:selection>
            <iffy:recent since="2024-08-16T22:22:14.297722-04:00" last="10" operator="and"/>
          </iffy:selection>
        </iffy:curation>
        <!-- Other channel elements -->
        <item>
          <!-- Other item elements -->
        </item>
      </channel>
    </rss>

#### Example (arbitrary query):

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/">
      <channel>
        <title>tech — interfluidity</title>
        <atom:link type="application/rss+xml" rel="self" href="https://tech.interfluidity.com/feed/index.rss"/>
        <iffy:curation>
          <iffy:selection>
            <acme:query> <!-- totally faking it here -->
              <acme:dbhost>articles.zine.dk</acme:dbhost>
              <acme:dbport>5432</acme:dbhost>
              <acme:sql>SELECT article_id FROM article WHERE author = 'Jane Doe'</acme:sql>
            </acme:query>
          </iffy:selection>
        </iffy:curation>
        <!-- Other channel elements -->
        <item>
          <!-- Other item elements -->
        </item>
      </channel>
    </rss>

## Element — `iffy:single`

### When beneath `iffy:curation`

`iffy:single` is a curation type, a description of how the feed is curated relative to the body of work a subset of which it presents.

Curation type `iffy:single` signifies that this is single-item RSS.

The feed contains just one item, not by happenstance because there is only one recent item, nor because some selection yielded just one item, but intentionally, so that metadata related to the item can have its own permanent RSS home.

#### Example:

    <?xml version='1.0' encoding='UTF-8'?>

    <rss version="2.0" xmlns:iffy="http://tech.interfluidity.com/xml/iffy/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/">
      <channel>
        <title>tech — interfluidity</title>
        <atom:link type="application/rss+xml" rel="self" href="https://tech.interfluidity.com/feed/index.rss"/>
        <iffy:curation>
          <iffy:single/>
        </iffy:curation>
        <!-- Other channel elements -->
        <item>
          <!-- Other item elements -->
        </item>
      </channel>
    </rss>

## Element — `iffy:synthetic`

This element marks channels or items that are in some sense automated or "synthetic".

SHOULD contain an `iffy-type`, and then other type-specific subelements.

### When a subelement of `channel`

`channel` > `iffy:synthetic` implies that ALL of the items in the channel are synthetic or automatically produced. An aggregation or curation of human-authored items SHOULD NOT be marked `iffy:synthetic`.

Known types:

- `ItemUpdateFeed` — A synthetic feed announcing updates of a particular logical item from another feed.

### When a subelement of `channel` AND `iffy:type` is `ItemUpdateFeed`

SHOULD include an `atom:link` with `rel` attribute set to `related`, pointing to the same resource as the `link` element of the item whose updates are being announced.

#### Example:

      <channel>
        <!-- other channel elements -->
        <iffy:synthetic>
          <iffy:type>ItemUpdateFeed</iffy:type>
          <atom:link rel="related" href="https://tech.interfluidity.com/xml/iffy/index.html"/>
        </iffy:synthetic>
      </channel>

### When a subelement of `item`

The `iffy:synthetic` element of an `item` SHOULD contain — in some form of parsable XML — all the data from which the item content (as reflected in `item` > `content:encoded` or `item` > `atom:content`) has been generated.

Consumers may opt to ignore these content items, and use the data from `iffy:synthetic` for custom renderings or further processing.

Known types:

- `UpdateAnnouncement` — A synthetic item marking an update of an older item in the feed (or that once would have been in the feed)
- `UpdateCumulation` — A synthetic item describing an aggregation of updates, which may include updates of multiple items, and multiple updates for each item.

### When a subelement of `item` AND `iffy:type` is `UpdateAnnouncement`

In addition to `iffy:type`, MUST contain an `iffy:update` element, which in turn MUST contain an `iffy:initial` element describing the initial state of the updated post.

#### Example:

    <item>
      <pubDate>Thu, 20 Jun 2024 13:10:00 -0400</pubDate>
      <guid isPermalink="true">
        https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index-updated-2024-06-20-13-10-00.html
      </guid>
      <link>https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index-updated-2024-06-20-13-10-00.html</link>
      <title>Updated: Feedletter tutorial</title>
      <!-- other item elements -->
      <iffy:synthetic>
        <iffy:type>UpdateAnnouncement</iffy:type>
        <iffy:update>
          <atom:updated>2024-06-20T17:10:00Z</atom:updated>
          <atom:summary>
            <![CDATA[Add note to Section 16, "Advanced: Customize the content" documenting <i>feedletter</i> API changes that slightly modify this section of the tutorial.]]>
          </atom:summary>
          <iffy:revision>
            https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index-oldcommit-acb84c08c1bbcc83036b9cad70f6a3c5d60865c4.html
          </iffy:revision>
          <iffy:diff>
            https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index-diff-acb84c08c1bbcc83036b9cad70f6a3c5d60865c4-to-current.html
          </iffy:diff>
          <iffy:initial>
            <atom:title><![CDATA[Feedletter tutorial]]></atom:title>
            <atom:link href="https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index.html"/>
            <iffy:uid>https://tech.interfluidity.com/2024/01/29/feedletter-tutorial/index.html</iffy:uid>
            <atom:published>2024-01-29T15:30:00Z</atom:published>
            <dc:creator><![CDATA[Steve Randy Waldman]]></dc:creator>
          </iffy:initial>
        </iffy:update>
      </iffy:synthetic>
      <dc:creator><![CDATA[Update-o-Bot]]></dc:creator>
      <content:encoded><!-- generated HTML content --></content:encoded>
    </item>

## Element — `iffy:type`

In general, marks the "type" of its containing element.

### When a subelement of `channel` > `iffy:synthetic`

Marks what kind of synthetic channel its parent is. Currently known values include

- `ItemUpdateFeed` — A synthetic feed announcing updates of a particular logical item from another feed.

### When a subelement of `item` > `iffy:synthetic`

Marks what kind of synthetic item its parent is. Currently known values include

- `UpdateAnnouncement` — A synthetic item marking an update of an older item in the feed (or that once would have been in the feed)

- `UpdateCumulation` — A synthetic item describing an aggregation of updates, which may include updates of multiple items, and multiple updates for each item.

Please see known containing elements, including

- `iffy:synthetic`.

## Element — `iffy:uid`

Refers to the `guid` of an `item` from a different item or construct.

Note: We define an `iffy:uid` element, rather than rely upon `atom:id`, because `atom:id` requires that its contents be an IRI, but we mean to impose no such restriction.

Please see known containing elements, including

- `iffy:initial`.

## Element — `iffy:update`

In general, describes or announces updates to previously published items.

Typo fixes, small rephrasings, and other tweaks are not expected to be recorded as distinct updates. That is, within a "single update" there may be a sequence of smaller revisions that go unrecorded.

Applications that want a more forensic history might consider including and exposing every published change in version control.

### When a sub-element of `item` > `iffy:update-history`

MUST contain one `atom:updated` element.

MAY also contain one each of

- `atom:summary`
- `iffy:diff`
- `iffy:revision`

MAY contain an `atom:title` element, if the title has been revised since a previous version

MAY contain any number of `dc:creator` elements, reflecting authorship specific to this revision.

By default, an update's title and authors are the same the containing item, which always reflects the current revisions authors.

If the title changes, or authorship is evolving over time, these items should be specified in every update that alters them.

The initial title and authorship SHOULD BE specified in an `iffy:initial` element if either have been revised.

See `iffy:update-history` example.

### When a sub-element of `item` > `iffy:synthetic` with `iffy:type` `UpdateAnnouncement`

MUST contain one `atom:updated` element.

MUST contain an `iffy:initial` describing the initial state of the item updated.

(Information in the containing `item` refers to the update announcement rather than the post whose update is announced, so an `iffy:initial` element is necessary.

MAY also contain one each of

- `atom:summary`
- `iffy:diff`
- `iffy:revision`

MAY contain an `atom:title` element, if the title has been revised since a previous version.

MAY contain any number of `dc:creator` elements, if authorship has been revised since a previous version..

## Element — `iffy:update-history`

### When an `item` level element

MUST contain a sequence of `iffy:update` elements, in reverse chronological order, describing the histories of major revisions to an item.

MAY contain one `iffy:initial` element.

Items containing an `iffy:update-history` SHOULD also include an `atom:updated` tag corresponding to the most recent update.

Typo fixes, small rephrasings, and other minor tweaks are not expected to be recorded as distinct updates. That is, within a "single update" there may be a sequence of smaller revisions that go unrecorded. Applications that want a more forensic history might consider including and exposing every published change in version control.

#### Example:

    <item>
      <!-- Other item elements -->
      <iffy:update-history>
        <iffy:update>
          <atom:updated>2024-06-02T04:20:00Z</atom:updated>
          <atom:summary>
            <![CDATA[Drop <code>iffy:timestamp</code>. We can just reuse <code>atom:updated</code> for the same work.]]>
          </atom:summary>
          <iffy:revision>
            https://tech.interfluidity.com/xml/iffy/index-oldcommit-199e44561de3fd9e731a335d8b2a655f42d9bc04.html
          </iffy:revision>
          <iffy:diff>
            https://tech.interfluidity.com/xml/iffy/index-diff-199e44561de3fd9e731a335d8b2a655f42d9bc04-to-current.html
          </iffy:diff>
        </iffy:update>
        <iffy:update>
          <atom:updated>2024-06-02T01:35:00Z</atom:updated>
          <atom:summary><![CDATA[Add initial take on tags related to updates and revisions.]]></atom:summary>
          <iffy:revision>
            https://tech.interfluidity.com/xml/iffy/index-oldcommit-72eaf9fdfebc9e627bff33bbe1102d4d250ad1d0.html
          </iffy:revision>
          <iffy:diff>
            https://tech.interfluidity.com/xml/iffy/index-diff-72eaf9fdfebc9e627bff33bbe1102d4d250ad1d0-to-199e44561de3fd9e731a335d8b2a655f42d9bc04.html
          </iffy:diff>
        </iffy:update>
        <iffy:update>
          <atom:updated>2024-05-26T03:00:00Z</atom:updated>
          <atom:summary><![CDATA[Add JS/CSS so that prior revisions are visually distinct from current.]]></atom:summary>
          <iffy:revision>
            https://tech.interfluidity.com/xml/iffy/index-oldcommit-13de0232319ceab2f830591c318089d18cbec78d.html
          </iffy:revision>
          <iffy:diff>
            https://tech.interfluidity.com/xml/iffy/index-diff-13de0232319ceab2f830591c318089d18cbec78d-to-72eaf9fdfebc9e627bff33bbe1102d4d250ad1d0.html
          </iffy:diff>
        </iffy:update>
        <iffy:update>
          <atom:updated>2024-05-24T04:25:00Z</atom:updated>
          <atom:summary>
            <![CDATA[Drop tags <code>iffy:when-updated</code> and <code>iffy:original-guid</code>, bad appraoch to updates.]]>
          </atom:summary>
          <iffy:revision>
            https://tech.interfluidity.com/xml/iffy/index-oldcommit-394986cb8d9c57f567d324e691a44d50102101ce.html
          </iffy:revision>
          <iffy:diff>
            https://tech.interfluidity.com/xml/iffy/index-diff-394986cb8d9c57f567d324e691a44d50102101ce-to-13de0232319ceab2f830591c318089d18cbec78d.html
          </iffy:diff>
        </iffy:update>
      </iffy:update-history>
    </item>

### When a sub-element of `iffy:synthetic` with `iffy:type` `UpdateCumulation`

MUST contain a sequence of `iffy:update-history` elements, each of which contains `iffy:update` elements in reverse chronological order, describing a sequence of major revisions to an item, and MUST ALSO contain one `iffy:initial` element, which MUST include an `iffy:uid` element identifying and describing the `item` whose updates are documented. See discussion under `iffy:initial`

← Names too on the nose
↑↑↑
Green shoots of sprouts →

### Major revisions:

- 2025-08-30 @ 06:50 PM EDT — Revise definition of curation, so it has only three types: all, selection, and single. iffy:recent becomes a query under selection. (diff)
- 2024-12-22 @ 10:40 AM EST — Document `iffy:item-ref` and `iffy:in-reply-to`. (diff)
- 2024-11-15 @ 01:10 AM EST — Document `iffy:curation`, and curation type elements `iffy:all`, `iffy:recent`, `iffy:selection`, `iffy:single`. (diff)
- 2024-11-02 @ 05:15 PM EDT — Clarifications of iffy:provenance and iffy:update-history. (diff)
- 2024-07-01 @ 02:40 PM EDT — Major revision of `iffy:synthetic`, generalize `iffy:initial`, `iffy:update`, `iffy:update-history`, define `iffy:uid`. (diff)
- 2024-06-20 @ 11:05 AM EDT — Document `iffy:type`, update documentation of `iffy:synthetic` as optionally including `iffy:type`. (diff)
- 2024-06-17 @ 11:50 PM EDT — Document `iffy:synthetic`. (diff)
- 2024-06-11 @ 02:10 PM EDT — Document `iffy:hint-announce`, `iffy:policy`, and `iffy:restriction`. (diff)
- 2024-06-02 @ 12:25 AM EDT — Drop `iffy:timestamp`. We can just reuse `atom:updated` for the same work. (diff)
- 2024-06-01 @ 09:35 PM EDT — Add initial take on tags related to updates and revisions. (diff)
- 2024-05-25 @ 11:00 PM EDT — Add JS/CSS so that prior revisions are visually distinct from current. (diff)
- 2024-05-24 @ 12:25 AM EDT — Drop tags `iffy:when-updated` and `iffy:original-guid`, bad appraoch to updates. (diff)
- 2024-05-13 @ 04:10 AM EDT — Initial publication.

Timestamps represent "major", substantative revisions. There may have been subsequent typo fixes and language reworkings within a major revision, after the time displayed. For a more complete and fine-grained update history, you can view the git repository commit history. The most recent minor modification of this entry occurred 2025-08-30 @ 06:50 PM EDT.