Engine Status

There is no browser to borrow from on the Switch. Brewser's DOM tree, CSS cascade, and layout engine are hand-reimplemented in TypeScript (~26K lines) running on top of the nx.js/V8 + Skia foundation (see Architecture). It's a genuine cascade and a genuine layout engine, not a shim — deep where real pages and libraries exercise it, shallower in the less-common corners of the spec.

Overall: roughly 70–75% of the "real-world app" surface. This page is the honest map of where each pillar stands. It's updated with each release, and the gap lists below double as the contribution roadmap.

What to expect

Works very well today: hand-written pages, jQuery-era scripts, forms, and canvas/WebGL apps.

Will break today: libraries that lean on capture-phase event listeners, el.closest() / complex querySelector, position: sticky, flex-wrap, or CSS transitions/filters.

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 — ~75%

Solid / production-grade:

• Tree mutation: appendChild / removeChild / insertBefore / replaceChild / append / prepend / remove / insertAdjacentHTML — all with fragment spreading, MutationObserver notification, and paint notify
• innerHTML parses real markup (not just text), outerHTML (get-only), textContent, cloneNode
• Attributes + dataset (full Proxy), classList, getElementById / getElementsByClassName / getElementsByTagName
• Geometry: getBoundingClientRect, offset* / client* / scroll*, scrollIntoView
• MutationObserver (tier-1, wired at every mutation site)

Notable gaps:

• closest() and matches() are absent
• nextElementSibling / previousElementSibling / firstElementChild etc. missing
• querySelector only matches a single simple selector (#id, .class, tag, [attr=v]) — no combinators, compound selectors, or pseudo-classes. The CSS engine itself understands all of those; that richer matcher just isn't exposed to querySelector yet
• Events have no capture phase; once / passive / capture options are ignored; bubbling works but event.target isn't retargeted

HTML — ~70%

Parser: tag-soup-tolerant subset — no spec tokenizer / insertion modes, but handles void elements, self-closing tags, all attribute quoting styles, comments, raw-text elements (<script> / <style>), numeric plus ~90 named entities, and reasonable error recovery.

Element coverage is broad: structural and semantic tags, inline text tags, real <table> layout, img / canvas / inline SVG / video / audio / iframe, details / summary, dialog, meter / progress.

Forms are the most complete area: input types text / password / email / checkbox / radio / range / color / date / time / number / file / hidden / button, full <select> (optgroup, multiple), <textarea>, <label for>.

Gaps:

• CDATA is broken; small named-entity table; comments and doctype are discarded; no <template> content model
• POST forms navigate with no request body (GET is fully implemented); no <datalist> / <fieldset> chrome
• Inline SVG supports translate-only transforms — no <text>, gradients, or filters
• <video> has no subtitle tracks
• iframe sandbox / CSP attributes are parsed but not enforced (treated as same-origin)

CSS — ~70%

Selectors & cascade — strongest area, ~82%:

• Full selector syntax including all combinators, the :nth-child family (proper an+b), :not(), :hover / :focus / :checked / :disabled / :empty, ::before / ::after with content: attr()
• Real specificity + source order, !important, UA default stylesheet
• CSS variables, calc() / min() / max() / clamp(), @media, @font-face, @keyframes
• Gaps: no @supports / @import / @layer / @container; ::placeholder / ::marker / ::selection unsupported

Layout — ~65%: block / inline / inline-block, Flexbox ~70%, Grid ~60%, tables ~40%, float, and all positioning (static / relative / absolute / fixed).

• Gaps: no flex-wrap, no position: sticky, no margin collapsing, no align-self / align-content, no grid template-areas / auto-fill, no table colspan / rowspan

Visual — ~65%: colors, linear/radial gradients, background-image, box-shadow, border-radius (uniform), opacity, z-index / stacking, real overflow scrolling, object-fit, 2D transforms (translate / rotate / scale), writing-mode.

• Gaps: no transition, no filter / backdrop-filter, no 3D / skew / matrix transforms, no outline, no non-solid border styles, no clip-path

Units — ~80%: px, %, em / rem, vw / vh (+ dvh / svh), vmin / vmax, ch, auto, env(), calc(). Physical units (cm / mm / pt) are dropped.

Summary

Related

• Web Platform Support — the JavaScript APIs and standards Brewser implements
• Graphics — Canvas 2D and WebGL, which sit beside this engine
• Known Limitations — the shorter list of the biggest current gaps
• Roadmap — where the gaps above are headed next

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Last updated for Brewser v1.0.0 — September 2026. Percentages are honest estimates of real-world surface coverage, not spec-section counts.