HTML API: Update customizable <select> parsing #9298

sirreal · 2025-07-22T07:56:48Z

Trac ticket: #63736

The HTML standard is being updated to support customizable select elements. The HTML API should be updated to account for the new changes.

WHATWG/HTML PR 10548 had landed with the updates. Several browsers already have support and MDN pages have been updated for select, selectedcontent, and a new guide on customizable select elements.

There's also an html5-lib tests PR that updates tests to account for the changes.

Update HTML API parsing to account for changes in whatwg/html#10548.

Apply html5lib/html5lib-tests#178.

Todo:

Update the html5lib-tests README and sha when the PR lands.

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

html5lib/html5lib-tests#178

Remove SELECT case and update comments numbers. The SELECT case was removed from the algorithm in the standard.

This was removed from the HTML standard

These insertion modes are removed from the standard.

See https://github.com/html5lib/html5lib-tests/pull/178/files?show-viewed-files=true&file-filters%5B%5D=#r2222195057

github-actions · 2025-07-22T11:31:05Z

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When SELECT > BUTTON > SELECTEDCONTENT is encountered, the selected option may need to be cloned into the SELECTEDCONTENT. The HTML processor does not support this action as it may require out of order processing.

github-actions · 2025-07-22T12:45:03Z

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sirreal · 2025-07-22T15:35:35Z

This can be tested with the HTML API Debugger.

html5lib/html5lib-tests@5ad026d

sirreal · 2025-09-10T11:26:31Z

The html5lib-tests updates were merged: html5lib/html5lib-tests#178

dmsnell

It’s taken me some time but I reviewed the changes to the HTML Spec and compared against this and I appreciate the thoroughness with which you implemented them.

I wanted before to add a reference to the spec version. This would be good to add here, so someone can cross-reference historically when the changes appeared. This can go in the module or class docblock I think.
We can put this into 6.9, so {WP_VERSION} can be updated.
Let’s review and harmonize all of the deprecations, both in coordinating the docblock annotations with the call to _deprecated_function() and in emptying things like the select scope code.

Not yet have I reviewed this against the SELECTEDCONTENT changes, but I think we will be able to largely ignore the semantics, since that appears at render time by the browser. It may be worth adding a note in the class docs indicating the level of support.

dmsnell · 2025-07-29T15:27:37Z

src/wp-includes/html-api/class-wp-html-open-elements.php

 	 *
 	 * @param string $tag_name Name of tag to check.
 	 * @return bool Whether the given element is in SELECT scope.
 	 */
 	public function has_element_in_select_scope( string $tag_name ): bool {
+		_deprecated_function( __METHOD__, '{WP_VERSION}' );


I still don’t know how the docblock tag and the function call interact. Do you feel like you have a strong understand? Are both expected/appropriate?

dmsnell · 2025-09-10T13:49:51Z

src/wp-includes/html-api/class-wp-html-open-elements.php

 	 *
 	 * @param string $tag_name Name of tag to check.
 	 * @return bool Whether the given element is in SELECT scope.
 	 */
 	public function has_element_in_select_scope( string $tag_name ): bool {
+		_deprecated_function( __METHOD__, '{WP_VERSION}' );


I think we should also be able to remove the body from this function and always return false since the actual select scope no longer exists

dmsnell · 2025-09-10T13:53:53Z

src/wp-includes/html-api/class-wp-html-processor.php

+				 * >   1. Parse error.
+				 * >   2. Ignore the token.
+				 */
+				if ( null !== $this->context_node && 'SELECT' === $this->context_node->node_name ) {


we appear to be inconsistent here, but I think I have tried to use isset( $this->context_node ) over null checks.

dmsnell · 2025-09-10T14:03:26Z

src/wp-includes/html-api/class-wp-html-processor.php

+			 * > An end tag whose tag name is "option"
+			 *
+			 * The "option" end tag is handled in the any other end tag section below.
+			 */


do we need this comment here? I am guessing it was added because it used to be in the code as a specific case but now it isn’t? If so, I don’t see a reason to duplicate the description that it’s handled by the catch-all.

dmsnell · 2025-09-10T17:25:01Z

My reading on this is that when we close an OPTION element we check if we are the first element with selected and that the parent SELECT is not a multiple.

If that’s the case we should be able to infer that we are inside a SELECTEDCONTENT and fib it, should we want to. This is something we could possibly track through a boolean flag in the parser.

Interesting the spec reads like this cloning only occurs when encountering an end tag whose name is OPTION. That’s not what Chrome is doing, because it clones the element when there are no closing tags. It’s like they are doing it upon the event of closing the OPTION instead of encountering the end tag.

Apply patch from <select> parser PR

aaee111

html5lib/html5lib-tests#178

sirreal self-assigned this Jul 22, 2025

sirreal added 12 commits July 22, 2025 10:11

Update reset_insertion_mode_appropriately

9ab745d

Remove SELECT case and update comments numbers. The SELECT case was removed from the algorithm in the standard.

Deprecate the has_element_in_select_scope method

1acfce7

This was removed from the HTML standard

Update "normal" end tag handling to include SELECT

aac853d

Update INPUT handling to account for SELECT

89c113d

Update HR tag handling

f75a08f

Update SELECT insertion handling

099f013

Update OPTION, OPTGROUP insertion handling

7fe3598

Remove in_select and in_select_in_table step methods

20e0807

These insertion modes are removed from the standard.

Deprecate unused insertion mode constants

45edeae

Adjust html5lib-test expectation

446cdaa

See https://github.com/html5lib/html5lib-tests/pull/178/files?show-viewed-files=true&file-filters%5B%5D=#r2222195057

Add close option tag comments, do not handle cloning

0ed0a68

Update has_element_in_scope with SELECT

8beb128

Bail when parsing SELECTEDCONTENT requiring clone

6be6287

When SELECT > BUTTON > SELECTEDCONTENT is encountered, the selected option may need to be cloned into the SELECTEDCONTENT. The HTML processor does not support this action as it may require out of order processing.

sirreal marked this pull request as ready for review July 22, 2025 12:44

sirreal requested a review from dmsnell July 22, 2025 12:44

Update html5lib-tests

9e79bb2

html5lib/html5lib-tests@5ad026d

sirreal mentioned this pull request Jul 22, 2025

HTML API: Plans for 6.9 WordPress/gutenberg#63037

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