Safari Technology Preview 252 adds named-feature() and lets SVG reach a filter in another file

Safari Technology Preview 252 was released on September 11, 2026 for macOS Golden Gate and macOS Tahoe, covering WebKit changes between 319252@main and 320112@main. The new features are spread across CSS, SVG, the Web API surface, WebAssembly, WebGPU and Web Inspector. Two of them continue the feature-detection work that arrived in the previous release.

What named-feature() actually tests

A feature query has grown one question at a time. @supports began by asking whether a declaration parses at all, then picked up selector(), font-tech() and font-format(), and in release 251 it gained at-rule(). This build adds named-feature(), which asks about something that has no syntax to test: a behavior the engine either implements or does not.

CSS Conditional Rules Module Level 5 defines the argument as an identifier drawn from a fixed registry, and that registry holds two entries. anchor-position-follows-transforms describes anchoring that accounts for the transforms on the anchor element itself, which an earlier draft did not do. single-axis-scroll-container describes a scroll container that scrolls in one axis while the other is clip; before that, clip beside a scrollable value computed to hidden, and hidden still counts as scrollable even though it draws no scrollbar.

The working group is blunt about not wanting the registry to grow. Its note says it intends to add features rarely, only where there is real demand to test something specific and no more general mechanism would cover the case. One way to read that is as an escape hatch for behavior changes the syntax cannot reveal, rather than a replacement for asking about a property.

Script gets an answer the media query already had

CSSMediaRule.matches is now supported. CSS Conditional Rules Module Level 3 defines it as returning true when the rule sits in a stylesheet attached to a document whose window matches that rule's media query. Code that wanted the same answer previously had to read conditionText and pass the serialized condition back through matchMedia().

CSSConditionRule.supports arrived in the same build. The release notes name it and say nothing more, and the published Conditional Rules drafts do not define it, so its exact behavior cannot be settled from the notes alone.

The rest of what is new

• user-select works without the vendor prefix.
• text-decoration-inset accepts percentage values.
• SVG takes text-overflow as a presentation attribute.
• SVG external resources work, so the url() reference can point at a filter, mask or gradient in another document.
• DOMException objects carry a stack property, matching other error objects.
• WebAssembly handles memory64 together with multiple memories.
• WebGPU accepts the snorm10-10-10-2 value of GPUVertexFormat.
• Web Inspector logs the site-specific quirks active on a page to the console.

Three removals that can break an existing stylesheet

margin-trim no longer accepts inline, inline-start or inline-end; the property now takes none | block | [ block-start || block-end ]. The flow-tolerance property from CSS Grid Lanes was renamed to fit-tolerance. And dominant-baseline lost use-script, no-change and reset-size, to match SVG 2.

A fourth change rewrites a result instead of removing a value. Simplification of calc() now turns clamp(none, a, b) into max(a, b) and clamp(a, b, none) into min(a, b), so anything that reads the computed value back will see the shorter form.