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Safari Technology Preview 253 is now available for macOS Golden Gate and macOS Tahoe, bringing a broad set of WebKit changes from revisions 320113@main through 321067@main. The preview adds several CSS and JavaScript capabilities while addressing rendering, accessibility, performance and media bugs.
More control over CSS timelines
The release expands scroll-driven animation support by allowing style-originated scroll timelines to match globally, including timelines defined outside the target’s hierarchy or an element governed by timeline-scope. It also adds CSSContainerRule.conditions and permits sibling-index() and sibling-count() in container query conditions.
Other CSS work covers safe and unsafe alignment combinations, extended numeric ranges for East Asian counter styles, and corrections to grid sizing, custom highlights, corner-shape, background painting and view-transition invalidation. These changes target layout and styling behavior that can affect complex responsive interfaces.
JavaScript and SVG changes
JavaScriptCore now supports BigInt values in Intl.PluralRules.prototype.select and selectRange, alongside a faster Toom-3 multiplication path for large BigInt values. The release also fixes issues involving regular-expression lookbehind, RegExp.escape, Temporal.ZonedDateTime rounding, typed arrays, bounds checks and stale JIT caches.
For graphics-heavy sites, SVG 2 path support is added to textPath, allowing text to follow an inline path without referencing a separate path element through href. Additional fixes cover SVG conditional processing, number attributes and rendering behavior.
Accessibility, performance and compatibility fixes
VoiceOver should now use macOS terminology for aria-keyshortcuts values and avoid repeatedly announcing streamed live-region content. WebKit also fixes excessive CPU and power use from large numbers of IntersectionObserver targets, long-URL navigation stalls and unnecessary full-layer repaints.
The notes include further corrections for Canvas, MediaRecorder, AV1 playback, file-backed Blob reads, HTTP header validation, PDF selection controls and several text, grid and compositing cases. Safari Technology Preview remains a testing channel, so developers should validate these behaviors in their own sites before relying on them broadly.
Source: Release Notes for Safari Technology Preview 253
SIGNAL TITANS
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