You know the STP release months that read like three grid fixes and a font-feature-settings tweak? This one is not that. STP 249 is a pile.
Safari Technology Preview 249 shipped on 2026-07-29, covering WebKit changes 316531@main through 317820@main, for macOS Golden Gate and macOS Tahoe. It is a preview build, not a stable Safari release. That framing matters for everything that follows.
The pile, laid out flat
Per the release notes, CSS gains under New Features: attr() function support, outline-offset: inset, the @function custom functions rule, if(), calc-mix(), and justify-self on block-level boxes. Under preview support: wrap-inside, text-decoration-inset, and content on the ::marker pseudo-element. HTML gains popover=hint. Web API gains close watchers, including the closedby attribute for dialog. JavaScript gains the Temporal object. WebGPU gains subgroups. The resolved-issues line names grid layout sizing, clip-path rendering, and highlight decoration layering.
That is nine CSS lines, two HTML/DOM lines, one JavaScript line and one WebGPU line in one preview build. The queue scored this drop a 92 for a reason.
