Safari Technology Preview 254 fixes four accessibility bugs and two broken animations

I'd retest 322472@main first ^[4]. Of the six accessibility and animation fixes, it is the only one where VoiceOver could not activate a control at all ^[17]. The bug let a CSS property meant for pointer input block a screen reader's press action on buttons, links and form controls ^[4].

The iOS error-message bug had a dry sort of thoroughness. A message built from several pieces of text was read in reverse order, with some of it repeated ^[6]. VoiceOver on iOS also failed to identify date, time and color inputs as pop-up buttons ^[3].

The animation fixes only show up under specific conditions, and a retest has to reproduce them. The opacity note limits the bug to accelerated animations ^[8]. A test page that never takes the accelerated path could pass on an affected build too. For the view timeline fix, the page needs a sticky-positioned inline ancestor and enough scroll for that ancestor to stick to the scroll container ^[7].

The build covers WebKit's main branch from 321068@main to 322634@main ^[2], a span of 1,566 identifiers ^[14]. The notes do not say which stable Safari release will pick these changes up. That gap matters most for the new features. Alongside interpolate-size, the build adds calc-size(), which allows calculations on intrinsic sizes such as auto, fit-content and max-content ^[10]. Both are listed as new features ^[9][10]. I'd keep them behind @supports on production pages until a stable release lists them.

Pages that reorder many grid items get a separate fix. Grid relayout cost had grown quadratically with the number of items carrying distinct order values ^[11].