Core Heading

PRC's override/extension of the WordPress core/heading block.

Block Namespace

prc-block/core-heading

Target Block: core/heading

What PRC Customizes

• Changes the default heading level from H2 to H4
• Adds "chapter/section" functionality for table of contents integration
• Adds an alternate TOC text attribute for overriding what appears in the table of contents
• Registers "Heading" (default, H4), "Section" (chapter heading), and "Layout Heading" variations
• Registers "Layout Heading", "Hidden", and Sub-title block styles
• Registers a Sub-title block binding that reads/writes the sub_title post meta field (replaces the deprecated prc-block/sub-title block)
• Cleans up auto-generated heading IDs (removes h- prefix, converts leading numbers to words)
• Generates reproducible IDs for headings without anchors
• Integrates chapter headings with prc-block/table-of-contents Interactivity API state
• Handles legacy chapter detection for posts published before March 2023
• Provides transforms from legacy [chapter] shortcode and prc-block/chapter block

Supports Modifications

None directly via supports. However, the default heading level is changed to 4 via block_type_metadata_settings.

Additional Attributes

Attribute	Type	Default	Description
isChapter	boolean	false	Marks the heading as a section/chapter heading for TOC inclusion
altTocText	string	''	Alternate text to display in the table of contents instead of the heading content
level	number	4	Heading level (H1–H6)
placeholder	string	''	Placeholder text in the editor when empty (Sub-title variation: "Add sub-title")

Registered both server-side (block_type_metadata) and client-side (blocks.registerBlockType).

Additional context consumed:

Context Key	Description
postId	Used for legacy chapter heading detection
prcLegacyChapter	Set to true for posts before March 2023

Available Styles

Style Name	Label	Description
layout-heading	Layout Heading	Black bottom border with 4px padding and 24px margin
hidden	Hidden	Visually hidden (0px font, 0 opacity, 0 height) on frontend; 50% opacity in editor
sub-title	Sub-title	Smaller, secondary heading style for post subtitles

Sub-title block binding

The deprecated prc-block/sub-title block was migrated to a bound core/heading with the Sub-title style. Producers insert a heading, apply the Sub-title style, and bind its content to the sub_title post meta field via the block bindings UI.

Binding source: prc-block/core-heading/sub-title (registered in block-bindings.js and class-core-heading.php).

Post meta: sub_title — registered with show_in_rest and single => true so the binding is editable in the block editor and persists through REST saves (including RTC).

Rendering rules (render_sub_title_heading):

• Bound headings outside core/post-content (e.g. in single templates) render the live sub_title meta value.
• Bound headings inside core/post-content are suppressed to avoid duplicating the template subtitle.
• Empty or whitespace-only meta renders nothing.

Migration: Legacy prc-block/sub-title blocks remain in deprecated/src/sub-title/ for backward compatibility. New content should use the bound heading pattern above.

Style Overrides

From style.scss:

Hidden style: On the frontend, headings with is-style-hidden (excluding editor context) get zero font size, zero opacity, zero height. In the editor, they display at 50% opacity.

Layout heading: is-style-layout-heading gets a 1px solid black bottom border, 4px bottom padding, 24px bottom margin.

Sub-title style: is-style-sub-title applies the secondary heading typography defined in style.scss (used by the sub-title block binding).

Legacy section-header: Same visual treatment as layout-heading (backward compatibility).

Sub-header alt: Black background with white text, display block.

Editor Enhancements

From index.js and controls.jsx:

• Wraps block edit with custom controls via createHigherOrderComponent
• Toolbar: Adds a book-alt icon toggle with labels Make Chapter / Remove Chapter to set isChapter. When turning a heading into a chapter, if getAnchorFromContent(content) yields a slug, the block also sets the anchor attribute so the fragment ID matches the heading text.
• Inspector Advanced Controls: When isChapter is true, shows an Alternate TOC Text text field (placeholder shows current heading content).
• Anchor sync (H3 and H4): For heading levels 3 and 4, a useEffect keeps the anchor attribute aligned with getAnchorFromContent(content) when the heading text changes or when the level switches into H3/H4 (same slug rules as below). Other levels do not receive automatic anchor updates from content.
• getAnchorFromContent (src/core-heading/utils.js): derives a URL slug from the raw RichText content — decode HTML entities, strip tags (inserting a space at tag boundaries so words do not run together), collapse whitespace, then cleanForSlug.
• Sub-title variation: the bound Sub-title heading variation sets placeholder: Add sub-title in the editor.
• Registers transforms from legacy blocks
• Registers three block variations

Frontend Interactivity

No dedicated view.js. Interactivity is handled server-side by injecting attributes on chapter headings that integrate with the prc-block/table-of-contents store.

PHP Rendering

Class: Core_Heading

Key behaviors:

1. ID cleanup: Removes h- prefix from auto-generated IDs. Converts leading numbers to words (e.g., h-5-things becomes five-things). Falls back to an MD5 hash of block content for reproducible IDs.
2. Legacy chapter detection: For the first heading in core/post-content, checks if the post date is before March 2023. If so, sets prcLegacyChapter context to true, which auto-marks H3 headings as chapters.
3. Table of contents integration: When isChapter is true:
   • Registers the heading in wp_interactivity_state('prc-block/table-of-contents') under sectionsFound
   • Uses altTocText as the TOC label if provided, otherwise strips tags from heading content
   • Adds data-is-section="true" attribute
   • Adds data-wp-interactive and data-wp-context for TOC interactivity
4. Context filter: check_if_legacy_chapter_heading runs once per post to determine legacy status, avoiding repeated database lookups.

Block Markup Example

<!-- Standard heading (H4 default) -->
<h4 class="wp-block-heading" id="survey-methodology">Survey Methodology</h4>

<!-- Chapter/section heading with TOC integration -->
<h3
	class="wp-block-heading"
	id="key-findings"
	data-is-section="true"
	data-wp-interactive='{"namespace":"prc-block/table-of-contents"}'
	data-wp-context='{"id":"key-findings"}'
>
	Key Findings
</h3>

<!-- Layout heading -->
<h3 class="wp-block-heading is-style-layout-heading">Related Reports</h3>

<!-- Hidden heading (accessibility only) -->
<h4 class="wp-block-heading is-style-hidden">Screen reader only text</h4>

Variations

Variation Name	Title	Description	Default Level
heading	Heading	Default heading variation	H4
section	Section	Chapter/section heading included in TOC	H3
layout-heading	Layout Heading	Heading with bottom border styling	H3

Transforms

Source	Type	Description
[chapter] shortcode	Shortcode	Converts [chapter title="..."] to H2 chapter heading
prc-block/chapter	Block	Converts legacy chapter block to heading with isChapter: true
core/shortcode containing [chapter]	Block	Extracts title and creates H2 chapter heading