Engine Status

There is no browser to borrow from on the Switch. Brewser's DOM tree, CSS cascade, and layout engine are reimplemented from scratch in TypeScript (~26K lines) running on top of the nx.js/V8 + Skia foundation (see Architecture). Overall, that from scratch engine (DOM, HTML, CSS) covers roughly 83% of the "real-world app" surface.

This page is the honest list of what's not done yet — the gap lists double as the contribution roadmap. The last two pillars, WebGL and Audio & Video, are bridge-backed rather than reimplemented, so they stand higher and their detail lives on their own pages. If an app or library breaks for you, file an issue with its name — real-world breakage reports directly shape what gets built next.

DOM (~84%)

children still includes text / comment nodes (spec is elements-only); the element-only accessors (firstElementChild / nextElementSibling / childElementCount …) are the correct-behaving alternative
outerHTML has no setter; document / window-level capture listeners aren't wired
dialog.showModal() has no focus trap or Esc-to-close; setPointerCapture doesn't reroute events

HTML (~80%)

No spec tokenizer / insertion modes: no <template> content model, no implicit <html> / <head> / <body> synthesis, comments and doctype are discarded (the parser is otherwise a tolerant tag-soup subset with error recovery)
No multipart/form-data request bodies (binary file upload); urlencoded GET + POST work. No <datalist> chrome
Inline SVG has no SMIL animation and only a filter subset (feGaussianBlur / feColorMatrix / feOffset / feDropShadow); filter-graph primitives (feComposite / feMerge / feTurbulence / feImage), gradientTransform / patternTransform, and spreadMethod reflect/repeat aren't modelled (<use> / <image> / patterns / markers / masks, shapes / paths / <text> / gradients / transform / viewBox are covered)
<video> has no subtitle (<track>) tracks; poster isn't loaded (a first-frame preview stands in)
iframe sandbox / CSP attributes are parsed but not enforced (treated as same-origin)

CSS (~84%)

Cascade: no @supports / @import / @layer / @container; ::placeholder / ::marker / ::selection pseudo-elements unsupported
Layout: vertical margin collapsing is contained — adjacent siblings, and a parent with its first / last in-flow block child through an open edge, collapse correctly (empty blocks self-collapse too), but a collapsed child margin never propagates out to become the parent's own outer margin, and clearance isn't modelled; grid has no grid-auto-flow: dense packing, named grid lines, or subgrid; tables support border-collapse: collapse (shared borders, pixel-exact for uniform widths — full width/style conflict resolution and border-spacing for the separate model are approximated / not modelled) but no nested-table promotion; position: sticky is vertical + page-level only (not inside nested scroll containers)
Visual: transform covers 2D (translate / rotate / scale), skew / matrix(), and 3D functions flattened to 2D (rotateX / rotateY foreshorten by cos θ, translate3d / scale3d use x,y, matrix3d uses its affine slice) — but no true 3D perspective / z-sorting (Canvas2D can't project), and transform-origin is fixed at the box centre. transition doesn't cover geometric properties (width / height / offsets) or transform: translate (those need per-frame relayout), and doesn't interpolate skew / matrix. CSS @keyframes animation interpolates translate (px + %), rotate / scale, opacity and colours (background / text), with animation-delay, animation-direction (normal / reverse / alternate) and timing functions — but not geometric box properties, animation-fill-mode, or comma-separated multi-animation lists. No clip-path. On rounded boxes the 3D border styles (groove / ridge / inset / outset) render as a solid stroke; backdrop-filter on moving (fixed / sticky) elements applies blur only (colour functions are skipped there to hold 60fps) and its backdrop excludes lower fixed / modal / scroll-container layers

WebGL 1 & 2 (~88%)

Bridge-backed, running straight on the Switch's Tegra X1 GPU — not a software reimplementation. WebGL 1 sits ~92% (the safest target), WebGL 2 ~85% and under active conformance hardening. Remaining gaps are exhaustive extension coverage and layered / 3D-texture sampling (GPU-driver-limited). Full extension lists and proof points: Graphics.

Audio & Video (~80%)

Bridge-backed: Web Audio on a hardware-backed graph (~70%), <audio> / <video> decode in software via FFmpeg (~85%). Remaining gaps are the Web Audio effect nodes (filter / convolver / delay / compressor), subtitle tracks, and hardware video decode. Full node list and codec matrix: Audio & Media.

Summary

Area	Complete	Biggest missing pieces
DOM	~84%	`children` elements-only, `outerHTML` setter, document/window capture listeners, `dialog` focus trap
HTML	~80%	spec parser (insertion modes / `<template>`), multipart form uploads, advanced SVG (SMIL animation / filter-graph primitives), iframe sandbox enforcement
CSS	~84%	3D-perspective transforms + `transform-origin`, geometric transitions / keyframes, `clip-path`, `@supports` / `@layer`
WebGL 1	~92%	exhaustive extension coverage
WebGL 2	~85%	layered / 3D-texture sampling (GPU-driver-limited), full conformance hardening
Audio & Video	~80%	Web Audio effect nodes (filter / convolver / delay / compressor), subtitle tracks, hardware video decode

Web Platform Support: the JavaScript APIs and standards Brewser implements
Graphics: Canvas 2D and WebGL, which sit beside this engine
Audio & Media: the Web Audio graph, media elements and codec matrix in full
Known Limitations: the shorter list of the biggest current gaps
Roadmap: where the gaps above are headed next

Last updated for Brewser v0.1.116, September 2026. Percentages are honest estimates of real-world surface coverage, not spec-section counts.