CSS support matrix

At a glance

NextPDF implements Cascading Style Sheets (CSS) rendering against published World Wide Web Consortium (W3C) specifications. Use this page to review every CSS module in NextPDF’s specification corpus and the truth-audited support state for that module in the rendering pipeline.

This revision comes from the Wave 4 B2 truth audit (plan section 4.4). The audit re-graded every row against real on-disk evidence (src/Html/, tests/, tests/Wpt/corpus/), the v8/v9 breaking-change architecture decision records (ADRs), and the internal CSS property coverage audit.

Four badges classify each row under the verification contract:

Verified — Implementation in src/Html/ plus a substantive dedicated automated fixture: either a property-level suite of three or more files under tests/Unit/Html/<Module>/, or a Web Platform Tests (WPT) corpus shard of fifty or more fixtures under tests/Wpt/corpus/. No per-CSS-module golden Portable Document Format (PDF) baseline is wired yet, so verified rows use the structural reproducibility profile (PHPUnit assertion equivalence), never bitwise.
Claimed — Module behavior is implemented in src/Html/ (source path cited), but the dedicated fixture is thin, shared, or absent. Each claimed row with a concrete implementation has a backfill issue.
Not supported — The static-PDF rendering pipeline does not include this module: runtime/browser-only APIs, scrolling/animation runtimes, and W3C-discontinued work. The row records the reason.
Unknown — The module is in the corpus, but the audit found no implementation or fixture evidence. The audit never guessed upward to improve the count.

The structural revision’s partial badge is retired: every former partial row was re-graded to claimed (implementation present, no dedicated fixture) or verified.

Legend

Badge	Meaning
`verified`	`src/Html/` + dedicated fixture suite (≥3 files) or WPT shard (≥50 fixtures); passes deterministically under the `structural` profile.
`claimed`	Implementation evidence in `src/Html/`, no dedicated fixture. Backfill issue tracked.
`not-supported`	Explicitly excluded from the static-PDF scope. Reason recorded.
`unknown`	No determinable evidence. Not guessed upward.

The Confidence column is an honest, non-binary signal for the evidence behind the stated badge (high / medium / low). It is independent of the badge itself.

Commitment statement

NextPDF supports the CSS modules listed below at the levels noted. Verified rows have a dedicated automated fixture suite or a substantive WPT corpus shard that asserts NextPDF’s behavior and passes deterministically under the structural reproducibility profile. Claimed rows have implementation evidence in src/Html/, but no dedicated fixture yet; each row is tracked by a backfill issue under tracking issue #614. Not supported rows document explicit scope boundaries for the static-PDF target.

No row claims byte-level reproducibility because this revision has no per-CSS-module golden PDF baseline. The verification contract forbids empty rows: when support cannot be determined, the row is unknown.

Audited counts (this revision)

Status	Modules	Confidence (high / medium / low)
Verified	12	8 / 4 / 0
Claimed	49	0 / 35 / 14
Not supported	67	62 / 5 / 0
Unknown	39	0 / 0 / 39
Total	167	70 / 44 / 53

The structural revision’s summary block was internally inconsistent: it declared 148 total (18 verified / 11 partial / 11 claimed / 53 not-supported / 55 unknown), while the file contained 167 module rows whose labels tallied to 34 verified / 13 partial / 13 claimed / 68 not-supported / 39 unknown. This audit corrected the total to the true 167 and re-graded every row against on-disk evidence: Verified dropped from a claimed 34 to a substantiated 12. The full before/after delta is in the in-repo _css-matrix-truth-report.md sidecar.

ADR accuracy corrections

The structural revision mislabeled three live capabilities as removed or not-supported. ADR-027 and ADR-028 removed only the ExperimentalFeature enum opt-in markers; the capabilities remain LIVE default-on:

Subgrid (css_grid_2) — LIVE; CssFeatureFlags::$layoutSubgrid default on. It was mislabeled “subgrid hard-removed v9.0.0”.
@container queries (css_contain_2) — runtime dispatch explicitly unchanged by ADR-028; flag opt-out preserved. It was mislabeled “hard-removed v9.0.0”.
writing-mode: vertical-lr (css_writing_modes_3) — default-on Stable since v7.0.0; ADR-027 graduated only the deprecation handshake. It was mislabeled “deprecated/removed v8.0.0”.

Data source

The machine-readable per-module rowset lives in the in-repo css-support-matrix-data.yaml, which is the source of truth. This page is the human-readable projection, grouped by category. Astro components consume the YAML data directly during the docs build.

Layout

W3C Module	Level	W3C	Status	Confidence
CSS Flexible Box Layout (`css_flexbox_1`)	1	CR	Verified	high
CSS Grid Layout (`css_grid_1`)	1	REC	Verified	high
CSS Grid Layout — Subgrid (`css_grid_2`)	2	CR	Claimed	medium
CSS Grid Layout — Masonry (`css_grid_3`)	3	ED	Not supported	high
CSS Display (`css_display_3`)	3	CR	Claimed	medium
CSS Display (`css_display_4`)	4	ED	Unknown	low
CSS Positioned Layout (`css_position_3`)	3	WD	Verified	high
CSS Positioned Layout (`css_position_4`)	4	ED	Unknown	low
CSS Box Alignment (`css_align_3`)	3	WD	Claimed	medium
CSS Box Sizing (`css_sizing_3`)	3	CR	Claimed	low
CSS Box Sizing (`css_sizing_4`)	4	ED	Unknown	low
CSS Box Model (`css_box_3`)	3	WD	Claimed	medium
CSS Box Model (`css_box_4`)	4	ED	Unknown	low
CSS Multi-column Layout (`css_multicol_1`)	1	CR	Claimed	medium
CSS Multi-column Layout (`css_multicol_2`)	2	ED	Unknown	low
CSS Fragmentation (`css_break_3`)	3	CR	Verified	medium
CSS Fragmentation (`css_break_4`)	4	ED	Unknown	low
CSS Containment (`css_contain_1`)	1	REC	Not supported	medium
CSS Containment — `@container` (`css_contain_2`)	2	CR	Claimed	low
CSS Containment (`css_contain_3`)	3	ED	Not supported	medium
CSS Inline Layout (`css_inline_3`)	3	WD	Claimed	medium
CSS Logical Properties (`css_logical_1`)	1	WD	Claimed	medium
CSS Page Floats (`css_page_floats_3`)	3	ED	Not supported	high
CSS Pagination Templates (`css_page_templates_3`)	3	ED	Not supported	high
CSS Exclusions (`css_exclusions_1`)	1	WD	Not supported	high
CSS Regions (`css_regions_1`)	1	WD	Not supported	high
CSS Template Layout (`css_template_1`)	1	NOTE	Not supported	high
CSS Layout API (`css_layout_api_1`)	1	WD	Not supported	high

Box model — backgrounds, borders, effects

W3C Module	Level	W3C	Status	Confidence
CSS Backgrounds and Borders (`css_backgrounds_3`)	3	CR	Claimed	medium
CSS Backgrounds (`css_backgrounds_4`)	4	ED	Unknown	low
CSS Borders and Box Decorations (`css_borders_4`)	4	ED	Unknown	low
CSS Gap Decorations (`css_gaps_1`)	1	ED	Unknown	low
CSS Masking (`css_masking_1`)	1	CR	Not supported	medium
CSS Shadow Module (`css_shadow_1`)	1	ED	Claimed	medium
CSS Shapes (`css_shapes_1`)	1	CR	Not supported	high
CSS Shapes (`css_shapes_2`)	2	ED	Not supported	high
Filter Effects (`filter_effects_1`)	1	WD	Not supported	high
Filter Effects (`filter_effects_2`)	2	ED	Not supported	high
Compositing and Blending (`compositing_1`)	1	CR	Claimed	medium
Compositing (`compositing_2`)	2	ED	Unknown	low
CSS Fill and Stroke (`fill_stroke_3`)	3	ED	Unknown	low
Geometry Interfaces (`geometry_1`)	1	CR	Not supported	high
DOMMatrix (`matrix`)	1	NOTE	Not supported	high
Motion Path (`motion_1`)	1	WD	Not supported	high

Typography — fonts, text

W3C Module	Level	W3C	Status	Confidence
CSS Fonts (`css_fonts_3`)	3	REC	Verified	medium
CSS Fonts (`css_fonts_4`)	4	CR	Verified	high
CSS Fonts (`css_fonts_5`)	5	ED	Unknown	low
CSS Font Loading (`css_font_loading_3`)	3	WD	Not supported	high
CSS Text (`css_text_3`)	3	CR	Claimed	medium
CSS Text (`css_text_4`)	4	ED	Claimed	medium
CSS Text Decoration (`css_text_decor_3`)	3	CR	Claimed	medium
CSS Text Decoration (`css_text_decor_4`)	4	ED	Unknown	low
CSS Ruby (`css_ruby_1`)	1	WD	Not supported	high
CSS Writing Modes (`css_writing_modes_3`)	3	REC	Claimed	medium
CSS Writing Modes (`css_writing_modes_4`)	4	ED	Unknown	low
CSS Speech (`css_speech_1`)	1	CR	Not supported	high
CSS Mobile Text Size Adjustment (`css_size_adjust_1`)	1	ED	Not supported	high

Color

W3C Module	Level	W3C	Status	Confidence
CSS Color (`css_color_3`)	3	REC	Claimed	medium
CSS Color (`css_color_4`)	4	CR	Claimed	medium
CSS Color (`css_color_5`)	5	WD	Unknown	low
CSS Color (`css_color_6`)	6	ED	Unknown	low
CSS Color Adjustment (`css_color_adjust_1`)	1	CR	Not supported	high
CSS Color HDR (`css_color_hdr_1`)	1	ED	Not supported	high
CSS Images (`css_images_3`)	3	CR	Claimed	medium
CSS Images (`css_images_4`)	4	ED	Unknown	low
CSS Images (`css_images_5`)	5	ED	Unknown	low
CSS Image Animation (`css_image_animation_1`)	1	ED	Not supported	high

Selectors, cascade, values

W3C Module	Level	W3C	Status	Confidence
CSS Selectors (`selectors_3`)	3	REC	Claimed	medium
CSS Selectors (`selectors_4`)	4	WD	Claimed	medium
CSS Selectors (`selectors_5`)	5	ED	Unknown	low
CSS Non-element Selectors (`selectors_nonelement_1`)	1	WD	Not supported	high
CSS Pseudo-Elements (`css_pseudo_4`)	4	WD	Claimed	medium
CSS Cascading and Inheritance (`css_cascade_3`)	3	REC	Verified	high
CSS Cascading (`css_cascade_4`)	4	CR	Verified	high
CSS Cascading (`css_cascade_5`)	5	CR	Verified	high
CSS Cascading (`css_cascade_6`)	6	WD	Unknown	low
CSS Values and Units (`css_values_3`)	3	REC	Claimed	medium
CSS Values and Units (`css_values_4`)	4	CR	Claimed	medium
CSS Values and Units (`css_values_5`)	5	ED	Unknown	low
CSS Custom Properties (`css_variables_1`)	1	CR	Claimed	medium
CSS Custom Properties (`css_variables_2`)	2	ED	Unknown	low
CSS Conditional Rules (`css_conditional_3`)	3	CR	Claimed	medium
CSS Conditional Rules (`css_conditional_4`)	4	ED	Unknown	low
CSS Conditional Rules (`css_conditional_5`)	5	ED	Unknown	low
CSS Conditional Values (`css_conditional_values_1`)	1	ED	Unknown	low
CSS Namespaces (`css_namespaces_3`)	3	REC	Claimed	low
CSS Style Attributes (`css_style_attr_1`)	1	CR	Claimed	medium
CSS Syntax (`css_syntax_3`)	3	CR	Claimed	medium
CSS Nesting (`css_nesting_1`)	1	CR	Claimed	medium
CSS Environment Variables (`css_env_1`)	1	ED	Not supported	medium
CSS Custom Functions and Mixins (`css_mixins_1`)	1	ED	Unknown	low
CSS Extensions (`css_extensions_1`)	1	NOTE	Unknown	low

Lists, counters, generated content

W3C Module	Level	W3C	Status	Confidence
CSS Lists and Counters (`css_lists_3`)	3	WD	Claimed	medium
CSS Counter Styles (`css_counter_styles_3`)	3	CR	Claimed	medium
CSS Generated Content (`css_content_3`)	3	WD	Claimed	medium
CSS Generated Content for Paged Media (`css_gcpm_3`)	3	WD	Claimed	medium
CSS Generated Content for Paged Media (`css_gcpm_4`)	4	ED	Unknown	low

Print / paged media

W3C Module	Level	W3C	Status	Confidence
CSS Paged Media (`css_page_3`)	3	WD	Claimed	medium
CSS Paged Media (`css_page_4`)	4	NOTE	Unknown	low
CSS Print Profile (`css_print`)	1	NOTE	Claimed	low
CSS Presentation Levels (`css_preslev_1`)	1	NOTE	Not supported	high

Overflow / scroll / UI

W3C Module	Level	W3C	Status	Confidence
CSS Overflow (`css_overflow_3`)	3	WD	Claimed	low
CSS Overflow (`css_overflow_4`)	4	ED	Unknown	low
CSS Overflow (`css_overflow_5`)	5	ED	Unknown	low
CSS Overscroll Behavior (`css_overscroll_1`)	1	CR	Not supported	high
CSS Scroll Anchoring (`css_scroll_anchoring_1`)	1	WD	Not supported	high
CSS Scroll Snap (`css_scroll_snap_1`)	1	REC	Not supported	high
CSS Scroll Snap (`css_scroll_snap_2`)	2	WD	Not supported	high
CSS Scrollbars Styling (`css_scrollbars_1`)	1	CR	Not supported	high
CSS Basic User Interface (`css_ui_3`)	3	REC	Not supported	medium
CSS Basic User Interface (`css_ui_4`)	4	WD	Not supported	high
CSS Form Control Styling (`css_forms_1`)	1	ED	Not supported	high
CSS View Transitions (`css_view_transitions_1`)	1	WD	Not supported	high
CSS View Transitions (`css_view_transitions_2`)	2	ED	Not supported	high
CSS Spatial Navigation (`css_nav_1`)	1	NOTE	Not supported	high
CSS Route Matching (`css_navigation_1`)	1	ED	Not supported	high

Tables

W3C Module	Level	W3C	Status	Confidence
CSS Table (`css_tables_3`)	3	WD	Verified	high

Transforms / animation / motion

W3C Module	Level	W3C	Status	Confidence
CSS Transforms (`css_transforms_1`)	1	CR	Claimed	medium
CSS Transforms (`css_transforms_2`)	2	ED	Unknown	low
CSS Animations (`css_animations_1`)	1	WD	Not supported	high
CSS Animations (`css_animations_2`)	2	ED	Not supported	high
CSS Transitions (`css_transitions_1`)	1	WD	Not supported	high
CSS Transitions (`css_transitions_2`)	2	ED	Not supported	high
CSS Easing Functions (`css_easing_1`)	1	CR	Not supported	high
CSS Easing Functions (`css_easing_2`)	2	ED	Not supported	high
Web Animations (`web_animations_1`)	1	WD	Not supported	high
Web Animations (`web_animations_2`)	2	ED	Not supported	high
Web Animations CSS Integration (`web_animations_css_integration`)	1	ED	Not supported	high
Animation Triggers (`animation_triggers`)	1	ED	Not supported	high
Pointer-driven Animations (`pointer_animations_1`)	1	ED	Not supported	high
Scroll-driven Animations (`scroll_animations_1`)	1	ED	Not supported	high
CSS Animation Worklet (`css_animation_worklet`)	1	ED	Not supported	high

Anchor / positioning extensions

W3C Module	Level	W3C	Status	Confidence
CSS Anchor Positioning (`css_anchor_position_1`)	1	WD	Unknown	low
CSS Anchor Positioning (`css_anchor_position_2`)	2	ED	Unknown	low
CSS Highlight API (`css_highlight_api_1`)	1	WD	Not supported	high
CSS Properties and Values API (`css_properties_values_api_1`)	1	CR	Not supported	high
CSS Painting API (`css_paint_api_1`)	1	WD	Not supported	high
CSS Typed OM (`css_typed_om_1`)	1	WD	Not supported	high
CSSOM (`cssom_1`)	1	WD	Not supported	high
CSSOM View (`cssom_view_1`)	1	WD	Not supported	high
CSS Will Change (`css_will_change_1`)	1	CR	Not supported	high
CSS Linked Parameters (`css_link_params_1`)	1	ED	Unknown	low
CSS Line Grid (`css_line_grid_1`)	1	NOTE	Unknown	low
CSS Rhythmic Sizing (`css_rhythm_1`)	1	ED	Unknown	low
CSS Round Display (`css_round_display_1`)	1	ED	Not supported	high
CSS Shaders (`css_shaders_1`)	1	NOTE	Not supported	high
CSS Viewport (`css_viewport_1`)	1	NOTE	Not supported	high

Media queries

W3C Module	Level	W3C	Status	Confidence
Media Queries (`mediaqueries_3`)	3	REC	Claimed	medium
Media Queries (`mediaqueries_4`)	4	CR	Claimed	medium
Media Queries (`mediaqueries_5`)	5	WD	Unknown	low

CSS 2 baseline

W3C Module	Level	W3C	Status	Confidence
CSS Level 2 (`css_2_1`)	2.1	REC	Claimed	low
CSS Level 2.2 (`css_2_2`)	2.2	NOTE	Claimed	low
CSS Snapshot 2026 (`css_snapshot_2026`)	snapshot	NOTE	Claimed	low

Non-CSS specifications (informational)

These W3C modules appear in the corpus but are outside the CSS rendering pipeline. When applicable, corresponding feature pages link to them.

W3C Module	W3C	Status	Confidence	Where
W3C SVG 1.1 (`svg_1_1`)	REC	Claimed	low	Inline SVG paint subset in `Renderer/PaintCommand/`; no CSS-matrix fixture.
W3C SVG 2.0 (`svg_2_0`)	CR	Unknown	low	Premium-pipeline concern; no core evidence.
W3C PNG 3rd Edition (`png_3`)	WD	Claimed	low	PNG decode in `Graphics/` module (outside HTML/CSS).
W3C WOFF 1.0 (`woff_1_0`)	REC	Claimed	low	WOFF via Font stack; no CSS-matrix fixture.
W3C WOFF 2.0 (`woff_2_0`)	REC	Claimed	low	WOFF2 via Font stack; no CSS-matrix fixture.
W3C WCAG 2.2 (`wcag_2_2`)	REC	Verified	medium	`src/Html/Aam/`, `tests/Unit/Accessibility/HtmlAam/` (4 files) — PDF/UA-2.
W3C WAI-ARIA 1.2 (`wai_aria_1_2`)	REC	Verified	medium	`tests/Unit/Accessibility/HtmlAam/` (4 files).
W3C ARIA Bundle (`w3c_aria_bundle`)	REC	Claimed	low	Guidance bundle; concrete evidence is the WAI-ARIA row.
W3C AAM Bundle (`w3c_aam_bundle`)	NOTE	Claimed	low	Bundle pointer; evidence is the WAI-ARIA/WCAG rows.
W3C ATAG 2.0 (`atag_2_0`)	REC	Not supported	high	Authoring-tool accessibility; not applicable.
W3C XSL 1.1 (`xsl_1_1`)	REC	Not supported	high	XSL-FO parallel formatting model; not implemented.
W3C XSD 1.1 Part 1 (`xsd_1_1_part1`)	REC	Not supported	high	XML schema; not applicable.
W3C XSLT 3.0 (`xslt_3_0`)	REC	Not supported	high	Transformation language; not applicable.
Resize Observer (`resize_observer_1`)	CR	Not supported	high	Browser runtime API.

Verification protocol

For a row to graduate from claimed → verified:

A dedicated property-level fixture suite lives under tests/Unit/Html/<Module>/ (≥3 files) or a substantive WPT corpus shard (≥50 fixtures) under tests/Wpt/corpus/ is promoted into an asserting test.
The fixture asserts NextPDF’s behavior against the W3C grammar for the module’s primary properties.
The fixture passes deterministically under a NextPDF\Testing\ReproducibilityProfile (structural for assertion fixtures; bitwise only once per-module golden PDF baselines exist).
The row’s nextpdf_status in the in-repo css-support-matrix-data.yaml flips to verified, with fixture_path, repro_profile, and confidence updated.

For a row to graduate from unknown → claimed:

An audit pass confirms implementation evidence in src/Html/ (cite the path in evidence + notes).
A backfill issue is opened and linked in backfill_issue.