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Browser support

Relements targets modern evergreen browsers. Support is two-tier, matching the HTML-first philosophy (see the HTML-first policy): a broad semantic HTML + CSS baseline, plus progressive enhancements that need recent engines and degrade gracefully where they are unavailable.

Tier 1 — Baseline (HTML + CSS)

Section titled “Tier 1 — Baseline (HTML + CSS)”

Semantic markup, design tokens, and component styles. The practical floor is cascade layers (@layer), which the stylesheet relies on.

EngineMinimum
Chrome / Edge99+
Firefox97+
Safari15.4+

(Roughly early 2022.) Below this, layered styles will not apply correctly. This tier also uses logical properties and native <dialog> styling, which are supported earlier than the floor above.

Tier 2 — Full enhanced experience

Section titled “Tier 2 — Full enhanced experience”

Some components use the newest platform features:

  • Popover API — <re-popover>, enhancePopover. Chrome 114+, Firefox 114+, Safari 17+.
  • :user-invalid validation styling — form fields. Chrome 118+, Firefox 116+, Safari 16.4+.
  • color-mix() — popover tonal backgrounds. Chrome 111+, Firefox 113+, Safari 16.4+.
EngineMinimum
Chrome / Edge118+
Firefox116+
Safari17+

(Roughly late 2023.)

Graceful degradation

Section titled “Graceful degradation”

Below Tier 2, the affected pieces fall back rather than break — the rest of the system (Tier 1) keeps working:

  • <re-popover> / enhancePopover no-op when the Popover API is absent (feature-detected); the markup stays valid.
  • Form validation styling falls back from :user-invalid to [aria-invalid="true"].
  • color-mix() surfaces fall back to their base token color.
  • The native <dialog> backdrop blur (backdrop-filter) is cosmetic; without it the backdrop is a solid scrim.

What we test

Section titled “What we test”

Every pull request runs the full suite — behavior, accessibility (axe), and visual regression — on Chromium, Firefox, and WebKit via Playwright (the current stable builds Playwright bundles). This is the actively verified guarantee; the version tables above document intent.

Not supported

Section titled “Not supported”
  • Internet Explorer.
  • Non-evergreen or end-of-life browsers below the Tier 1 floor.
Section titled “Related”