Support `<selectedcontent>` in `<select multiple>` by josepharhar · Pull Request #12430 · whatwg/html

josepharhar · 2026-05-08T22:58:41Z

This PR adds support for using the selectedcontent element in a select
element with the multiple attribute by cloning each of the option
elements into the selectedcontent element.

Each cloned option will be wrapped by a generated div element inside the
selectedcontent element, so the resulting DOM would look like this:

<select multiple size=1>
  <selectedcontent>
    <div>one</div>
    <div>two</div>
  </selectedcontent>
  <option selected>one</option>
  <option selected>two</option>
  <option>three</option>
</select>

Fixes #12342

At least two implementers are interested (and none opposed):
- Chrome
- …
- Standards positions:
  - Selectedcontent in select multiple WebKit/standards-positions#684
  - Selectedcontent in select multiple mozilla/standards-positions#1420
Tests are written and can be reviewed and commented upon at:
- https://wpt.fyi/results/html/semantics/forms/the-select-element/customizable-select-multiple-popup/selectedcontent-multiple.tentative.html
Implementation bugs are filed:
- Chromium: https://issues.chromium.org/issues/483769482
- Gecko: …
- WebKit: …
Corresponding HTML AAM & ARIA in HTML issues & PRs: not needed
MDN issue is filed: …
The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

/form-elements.html ( diff )

This PR improves the "clear a select's non-primary selectedcontent elements" algorithm by making it create a list of selectedcontent elements to modify separately from modifying them in order to prevent the list of elements to change while iterating. Fixes whatwg#11880

This PR makes sure that the contents of the selectedcontent element stay up to date when the selected option is changed in the selectedness setting algorithm. This issue was found here: web-platform-tests/wpt#55849 (comment)

In order to make the selectedness setting algorithm match implementations, this PR makes the selectedness setting algorithm avoid changing the selectedness of option elements which haven't ran their insertion steps yet by checking whether the options have their cached nearest ancestor select element assigned yet or not. This was discussed here: whatwg#11825

…electedcontentredo

…edcontentredo

…contentredo Merged the PRs, now I need to do the selectedcontent rewrite to clone into all descendant selectedcontent elements.

This PR adds support for using the selectedcontent element in a select element with the multiple attribute by cloning each of the option elements into the selectedcontent element. Each cloned option will be wrapped by a generated div element inside the selectedcontent element, so the resulting DOM would look like this: ```html <select multiple size=1> <selectedcontent> <div>one</div> <div>two</div> </selectedcontent> <option selected>one</option> <option selected>two</option> <option>three</option> </select> ``` Fixes whatwg#12342

josepharhar · 2026-05-08T23:01:05Z

This PR is currently based on the other PR to rewrite a bunch of selectedcontent stuff, and therefore includes all of its contents: #12263

When that PR is merged, the diff of this one should be easier to read.

Here is a diff which shows the actual changes of this proposal by diffing the other PR with this one: https://github.com/josepharhar/html/compare/selectedcontentredo...josepharhar:html:selectedcontentmultiple?expand=1

keithamus · 2026-05-12T16:09:05Z

+     <li><p>If <var>option</var> is <span data-x="concept-option-selectedness">selected</span>, then
+     <span data-x="list append">append</span> <var>option</var> to
+     <var>selectedOptions</var>.</p></li>
+    </ol>
+   </li>
+
+   <li><p>If <var>select</var> has the <code data-x="attr-select-multiple">multiple</code>
+   attribute, then run <span>clone multiple options into a <code>selectedcontent</code></span> given
+   <var>selectedOptions</var> and <var>selectedcontent</var>.</p></li>


Would it make more sense here to do something like:

Let isMulitple be true if select has the multiple attribute.

For each option in select's list of options.

If option is not selected then continue.

If isMultiple is false, run clone an option into a selectedcontent given option and selectedcontent, and return.

Append option to selectedoptions given selectedOptions and selectedcontent.

If selectedoptions is empty, then run clear a selectedcontent given selectedcontent.

Otherwise, run clone multiple options into a selectedcontent given selectedOptions and selectedcontent.

Thanks for the suggestion! The difference is that this algorithm can return earlier when it sees a selected option for a non-multiple select, right?

zcorpan · 2026-05-18T13:16:18Z

The performance cost during parsing could be pretty bad if the cloning of all selected options (seen so far) happens for every option end tag, right?

josepharhar · 2026-05-18T16:22:38Z

The performance cost during parsing could be pretty bad if the cloning of all selected options (seen so far) happens for every option end tag, right?

Agreed, thanks for catching that! I pushed a change to stop updating selectedcontent elements during option parsing if the select is multiple, and instead update them at the end of the select tag's parsing.

When a selected option element is done parsing, it triggers an update to the selectedcontent element of the associated select element. In the case of a select element with the multiple attribute, this could result in many clones if multiple options have the selected attribute. This change improves this by moving the selectedcontent update for select elements with the multiple attribute from option end tag parsing to select end tag parsing. Context: whatwg/html#12430 (comment) Bug: 483769482 Change-Id: I9ee8a2afe66884da26cbf814b80af7bf430414a6 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7856275 Reviewed-by: Mason Freed <masonf@chromium.org> Commit-Queue: Joey Arhar <jarhar@chromium.org> Reviewed-by: Joey Arhar <jarhar@chromium.org> Cr-Commit-Position: refs/heads/main@{#1636613}

…or select multiple, a=testonly Automatic update from web-platform-tests Improve selectedcontent parsing update for select multiple When a selected option element is done parsing, it triggers an update to the selectedcontent element of the associated select element. In the case of a select element with the multiple attribute, this could result in many clones if multiple options have the selected attribute. This change improves this by moving the selectedcontent update for select elements with the multiple attribute from option end tag parsing to select end tag parsing. Context: whatwg/html#12430 (comment) Bug: 483769482 Change-Id: I9ee8a2afe66884da26cbf814b80af7bf430414a6 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7856275 Reviewed-by: Mason Freed <masonf@chromium.org> Commit-Queue: Joey Arhar <jarhar@chromium.org> Reviewed-by: Joey Arhar <jarhar@chromium.org> Cr-Commit-Position: refs/heads/main@{#1636613} -- wpt-commits: 229f4c8b965b0fa27fee7167494173189163502b wpt-pr: 60193

…or select multiple, a=testonly Automatic update from web-platform-tests Improve selectedcontent parsing update for select multiple When a selected option element is done parsing, it triggers an update to the selectedcontent element of the associated select element. In the case of a select element with the multiple attribute, this could result in many clones if multiple options have the selected attribute. This change improves this by moving the selectedcontent update for select elements with the multiple attribute from option end tag parsing to select end tag parsing. Context: whatwg/html#12430 (comment) Bug: 483769482 Change-Id: I9ee8a2afe66884da26cbf814b80af7bf430414a6 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7856275 Reviewed-by: Mason Freed <masonfchromium.org> Commit-Queue: Joey Arhar <jarharchromium.org> Reviewed-by: Joey Arhar <jarharchromium.org> Cr-Commit-Position: refs/heads/main{#1636613} -- wpt-commits: 229f4c8b965b0fa27fee7167494173189163502b wpt-pr: 60193 UltraBlame original commit: 01575e0b302cb625cda91a07b144a9cabf2478a2

… changed in theory

…no more post-insertion needed

…edcontentmultiple

josepharhar added 25 commits November 4, 2025 13:02

Update selectedcontent in selectedness setting

5d4835a

This PR makes sure that the contents of the selectedcontent element stay up to date when the selected option is changed in the selectedness setting algorithm. This issue was found here: web-platform-tests/wpt#55849 (comment)

remove duplicate li

dd2258a

inline one step list

85ef15c

change variable names

80e0785

nits

dfec190

Merge branch 'main' into selectednesssetting

6b749d8

readability improvements

af049b7

rename variable

a51df08

Merge remote-tracking branch 'origin/selectedcontentiterating' into s…

8f410a4

…electedcontentredo

Merge remote-tracking branch 'origin/selectednesssetting' into select…

12e587c

…edcontentredo

Merge remote-tracking branch 'origin/selectednesscheck' into selected…

ff783fa

…contentredo Merged the PRs, now I need to do the selectedcontent rewrite to clone into all descendant selectedcontent elements.

Update all descendant selectedcontent elements

96c2613

re-merge selectedness setting algorithm

4b75042

inline loop

175b54c

in->of

5088085

,->;

a09e79c

Merge branch 'main' into selectedcontentredo

dae7e55

build list with only enabled selectedcontents

d095eb6

dont update selectedcontent in option insertion/removal steps

091d737

add missing display size check

86b46b3

remove unused variable and fix naming

277f9fa

only queue microtask if there is a selectedcontent element

57b0f75

josepharhar mentioned this pull request May 8, 2026

Selectedcontent in select multiple #12342

Open

annevk added the topic: select The <select> element label May 11, 2026

address review comments

9770048

keithamus reviewed May 12, 2026

View reviewed changes

josepharhar added 4 commits May 12, 2026 14:11

small fixes

d55c0ca

update selectedcontent after moving steps

fb7140c

a couple fixes

72f7660

Merge branch 'selectedcontentredo' into selectedcontentmultiple

a8886b4

improve selectedcontent parsing update for select multiple

b830618

chromium-wpt-export-bot mentioned this pull request May 27, 2026

Improve selectedcontent parsing update for select multiple web-platform-tests/wpt#60193

Merged

Merge branch 'main' into selectedcontentredo

d68af3e

annevk added 3 commits June 5, 2026 10:07

nits

b5c0c48

make post-connection steps recalculate as well as disabled could have…

5a4e27d

… changed in theory

This demonstrates what it would look like if we only did microtasks; …

a35e96a

…no more post-insertion needed

This was referenced Jun 9, 2026

Selectedcontent in select multiple WebKit/standards-positions#684

Open

Selectedcontent in select multiple mozilla/standards-positions#1420

Open

josepharhar added 2 commits June 10, 2026 13:53

any descendant selectedcontent check

eee149c

Merge remote-tracking branch 'origin/selectedcontentredo' into select…

4bb6f73

…edcontentmultiple

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Support `<selectedcontent>` in `<select multiple>`#12430

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