[Sukhendu2002]

What this PR does

Adds a structured API for generating and filtering inline <style> tags, mirroring the existing inline script tag API:

• Adds wp_get_inline_style_tag( $data, array $attributes = array() ).
• Adds wp_print_inline_style_tag().
• Adds the wp_inline_style_attributes filter, which receives the attributes and the CSS.
• Uses WP_HTML_Tag_Processor for safe attribute and CSS handling, including escaping of a closing </style> in the CSS.
• Documents $attributes as array<string, string|bool>, matching wp_get_inline_script_tag().

This allows plugins to add attributes such as CSP nonces without modifying complete HTML strings. The script portion of the original ticket is already covered by wp_inline_script_attributes, so this PR focuses on the remaining inline style functionality.

Usage in WP_Styles and script-loader.php

The WP_Styles output for normal, no-source, and concatenated inline styles, plus the hoisted extra block library styles and block support styles in script-loader.php, now go through the new API instead of building the tag with WP_HTML_Tag_Processor directly. This is the same way r61485 updated WP_Scripts along with the script tag functions.

Other STYLE tags

At the reviewer's request, the conversion of the other STYLE tags to the new API has been split into separate PRs, which depend on this one:

• Route core STYLE tags through the inline style tag API #14216: STYLE tags printed by core outside of WP_Styles (wp-admin and wp-includes).
• Bundled Themes: Route STYLE tags through the inline style tag API #14217: the bundled themes.

Testing

New tests in tests/phpunit/tests/dependencies/wpInlineStyleTag.php and tests/phpunit/tests/dependencies/styles.php use assertEqualHTML() and WP_HTML_Tag_Processor to verify the output.

Trac ticket: https://core.trac.wordpress.org/ticket/51325

Use of AI Tools

AI assistance: Yes
Tool(s): OpenAI Codex
Model(s): GPT-5.6
Used for: Initial code skeleton, test suggestions and code review; final implementation and tests were reviewed and edited by me.

Additional commits were made with Claude Code (Claude Opus 5.5) at the direction of @westonruter, to make the tests more robust with assertEqualHTML() and WP_HTML_Tag_Processor, to route the remaining core <style> tags through the new API (since split into #14216 and #14217), and to address code review findings. The changes were reviewed by @westonruter.

---

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.

🤖 Generated with Claude Code

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The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

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Props sukhendu2002, westonruter, jonsurrell, huubl.

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[sirreal]

The attribute filter here (and already existing on script tag function) should be passed the script tag data from the processor instead of the original data before setting.

[westonruter]

@Sukhendu2002 Do you want to action on Jon's feedback?

[sirreal]

Thanks, this looks good to me.

[westonruter]

I just found something problematic with this. By allowing the attributes to be filtered, it can result in the id being passed in to get dropped or modified. This can break things. For example, wp_custom_css_cb() constructs a STYLE tag with an id of wp-custom-css. In the Customizer JS, it looks for a STYLE with that id specifically to rewrite:

wordpress-develop/src/js/_enqueues/wp/customize/preview.js

Lines 654 to 670 in 8ce8797

	if ( api.settings.theme.isBlockTheme ) {
	style = $( 'style#global-styles-inline-css' );
	// Forbid milestone comments from appearing in Custom CSS which would break live preview.
	value = value.replace( /\/\*(BEGIN|END)_CUSTOMIZER_CUSTOM_CSS\*\//g, '' );
	var textContent = style.text().replace(
	/(\/\*BEGIN_CUSTOMIZER_CUSTOM_CSS\*\/)((?:.|\s)*?)(\/\*END_CUSTOMIZER_CUSTOM_CSS\*\/)/,
	function ( match, beforeComment, oldValue, afterComment ) {
	return beforeComment + '\n' + value + '\n' + afterComment;
	}
	);
	style.text( textContent );
	} else {
	style = $( 'style#wp-custom-css' );
	style.text( value );
	}

There are other integrations like this in PHP, for example in wp_hoist_late_printed_styles() it looks for a STYLE that has a specific id:

wordpress-develop/src/wp-includes/script-loader.php

Lines 4507 to 4531 in 8ce8797

	// Locate the insertion points in the HEAD.
	while ( $processor->next_tag( array( 'tag_closers' => 'visit' ) ) ) {
	if (
	'STYLE' === $processor->get_tag() &&
	'wp-global-styles-placeholder-inline-css' === $processor->get_attribute( 'id' )
	) {
	/** This is added in {@see wp_enqueue_global_styles()} */
	$processor->set_bookmark( 'wp_global_styles_placeholder' );
	} elseif (
	'STYLE' === $processor->get_tag() &&
	'wp-block-styles-placeholder-inline-css' === $processor->get_attribute( 'id' )
	) {
	/** This is added in {@see wp_enqueue_registered_block_scripts_and_styles()} */
	$processor->set_bookmark( 'wp_block_styles_placeholder' );
	} elseif (
	'STYLE' === $processor->get_tag() &&
	'wp-block-library-inline-css' === $processor->get_attribute( 'id' )
	) {
	/** This is added here in {@see wp_hoist_late_printed_styles()} */
	$processor->set_bookmark( 'wp_block_library' );
	} elseif ( 'HEAD' === $processor->get_tag() && $processor->is_tag_closer() ) {
	$processor->set_bookmark( 'head_end' );
	break;
	}
	}

This would break if the id is changed with a filter.

Perhaps the id should be considered immutable, that any changes are ignored. If the id being filtered doesn't match the initial id passed in, it could issue a _doing_it_wrong().

[westonruter]

This PR now has merge conflicts after r64585 which will need to be resolved.