# Safari Technology Preview 15 Release Notes Preview the latest web technology updates including: Fetch API, JavaScript, CSS, Web APIs, Web Inspector, Media, Accessibility, URL Handling, Security, and Safari Extensions. ## Overview [Safari Technology Preview](https://webkit.org/blog/6017/introducing-safari-technology-preview/) Release 15 is now [available for download](https://webkit.org/downloads/) for both macOS Sierra and OS X El Capitan 10.11.6. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. This release covers WebKit revisions [206196–206808](https://trac.webkit.org/log/?stop_rev=206196&rev=206808&limit=999). This is the last release of Safari Technology Preview that will install and run on OS X El Capitan. To continue testing or living on the latest enhancements to Safari and WebKit, please upgrade to macOS Sierra. ### Fetch API - Made `ReadableStream` throw `TypeError` values instead of strings ([r206770](https://trac.webkit.org/changeset/206770/)) - Changed Fetch to prevent redirection to non-HTTP URLs ([r206716](https://trac.webkit.org/changeset/206716/)) - Made `FetchBody` use UTF8 to encode text data ([r206636](https://trac.webkit.org/changeset/206636/)) - Added support for `URLSearchParams` as the `body` of a Fetch ([r206632](https://trac.webkit.org/changeset/206632/)) ### JavaScript - Sped up `String.prototype.toLowerCase()` by 7–8% on benchmarks ([r206804](https://trac.webkit.org/changeset/206804/)) - Fixed cases where class, function, and arrow function names were not inferred during assignment ([r206599](https://trac.webkit.org/changeset/206599/), [r206610](https://trac.webkit.org/changeset/206610/)) - Fixed arrow functions so they don’t allow duplicate parameter names ([r206647](https://trac.webkit.org/changeset/206647/)) - Updated `Generator` and `GeneratorFunction` property descriptors to match the ES6 spec ([r206711](https://trac.webkit.org/changeset/206711/), [r206738](https://trac.webkit.org/changeset/206738/)) - Fixed a bug where `String.prototype.padStart()` and `padEnd()` would insert `null` in rare cases ([r206573](https://trac.webkit.org/changeset/206573)) - Fixed a bug with `Function.prototype.length` when there are parameters with default values ([r206268](https://trac.webkit.org/changeset/206268/)) ### CSS - Implemented rendering of `font-variation-settings` and enabled it by default ([r206679](https://trac.webkit.org/changeset/206679/), [r206701](https://trac.webkit.org/changeset/206701/), [r206761](https://trac.webkit.org/changeset/206761/)) - Implemented animation of `font-variation-settings` ([r206690](https://trac.webkit.org/changeset/206690/)) - Added mapping for `font-family: cursive` to KaiTi fonts in Chinese ([r206791](https://trac.webkit.org/changeset/206791/)) - Sped up the computation of CSS Grid row sizes with indefinite heights by 2× ([r206253](https://trac.webkit.org/changeset/206253/)) - Fixed setting a style element’s `textContent` or `cssText` so it properly triggers a style recalculation ([r206404](https://trac.webkit.org/changeset/206404/)) - Fixed toggling `display: none` on a parent element of a Shadow DOM slot to work in more cases ([r206493](https://trac.webkit.org/changeset/206493/)) ### Web APIs - Enabled support for the `download` attribute on anchor and area elements — including Blob URLs ([r206356](https://trac.webkit.org/changeset/206356), [r206358](https://trac.webkit.org/changeset/206358/), [r206439](https://trac.webkit.org/changeset/206439/), [r206478](https://trac.webkit.org/changeset/206478/), [r206630](https://trac.webkit.org/changeset/206630/)) - Exposed `CryptoKey` to Web Workers ([r206627](https://trac.webkit.org/changeset/206627/)) - Implemented `Node.prototype.getRootNode()` ([r206285](https://trac.webkit.org/changeset/206285/)) - Implemented `ShadowRoot.prototype.elementFromPoint()` ([r206795](https://trac.webkit.org/changeset/206795/)) - Implemented `DOMTokenList.prototype.supports()` ([r206561](https://trac.webkit.org/changeset/206561/), [r206616](https://trac.webkit.org/changeset/206616/)) - Implemented `ImageData.prototype.data` from the HTML spec ([r206634](https://trac.webkit.org/changeset/206634/)) - Implemented `KeyboardEvent.prototype.code` from the UI Event spec ([r206803](https://trac.webkit.org/changeset/206803/)) - Implemented `KeyboardEvent.prototype.isComposing` from the UI Event spec ([r206796](https://trac.webkit.org/changeset/206796/)) - Implemented `KeyboardEvent.prototype.key` from the UI Event spec ([r206750](https://trac.webkit.org/changeset/206750/)) - Implemented `KeyboardEvent.prototype.repeat` from the UI Event spec ([r206724](https://trac.webkit.org/changeset/206724/)) - Implemented `KeyboardEvent.prototype.getModifierState()` from the UI Event spec ([r206725](https://trac.webkit.org/changeset/206725/)) - Changed `ReadableStream` to match the Steams API spec ([r206508](https://trac.webkit.org/changeset/206508/)) - Changed `DOMTokenList.prototype.value` and `toString()` to match the DOM spec ([r206560](https://trac.webkit.org/changeset/206560/)) - Changed `td.scope` to only return known values ([r206733](https://trac.webkit.org/changeset/206733/)) - Changed `HTMLLabelElement.prototype.form` to match the HTML spec ([r206332](https://trac.webkit.org/changeset/206332/)) - Changed `Element.insertAdjacentHTML()` to match the HTML spec ([r206308](https://trac.webkit.org/changeset/206308/)) - Changed `window.open()` so it returns `null` when it is blocked by Safari ([r206777](https://trac.webkit.org/changeset/206777/)) - Changed `HTMLSlotElement.prototype.assignedNodes()` to include fallback contents when `flatten` option is set ([r206534](https://trac.webkit.org/changeset/206534/)) - Changed `Object.prototype.getOwnPropertyDescriptor()` so it works correctly across origins ([r206221](https://trac.webkit.org/changeset/206221/)) - Changed HTML serialization to always add `xml:` prefix for attributes in the XML namespace ([r206663](https://trac.webkit.org/changeset/206663/)) - Changed properties on `Window` and `Location` to be non-enumerable when accessing them cross origin ([r206233](https://trac.webkit.org/changeset/206233/)) - Fixed a bug where text nodes assigned to a linked slot were not clickable ([r206605](https://trac.webkit.org/changeset/206605/)) - Fixed the assignment of non-numeric values to `input.minlength` by setting it to 0 ([r206588](https://trac.webkit.org/changeset/206588/)) - Fixed input elements so they work inside Shadow DOM trees ([r206403](https://trac.webkit.org/changeset/206403/)) - Fixed the `document.title` getter by stripping and collapsing the right whitespace characters ([r206309](https://trac.webkit.org/changeset/206309/)) - Fixed going into fullscreen from Silverlight a second time would hide the menu bar and dock for Safari ([r206675](https://trac.webkit.org/changeset/206675/)) - Fixed the serialization of HTML element attributes to match the HTML spec ([r206240](https://trac.webkit.org/changeset/206240/)) - Fixed the serialization of HTML void elements to ignore any child elements ([r206266](https://trac.webkit.org/changeset/206266/)) - Fixed the serialization of `bgsound`, `keygen`, and `track` elements ([r206246](https://trac.webkit.org/changeset/206246/)) - Fixed a bug where setting attributes on `HTMLMeterElement` to non-finite values would throw the wrong exception type ([r206243](https://trac.webkit.org/changeset/206243/)) - Fixed a bug where `IDBIndex.prototype.openCursor()` would match indices on multiple object stores ([r206280](https://trac.webkit.org/changeset/206280/)) - Fixed a bug preventing structured clones of `WebCrypto` keys under Safari 10 ([r206684](https://trac.webkit.org/changeset/206684)) ### Web Inspector - Added line range highlighting to show where the debugger is paused — good for lines with multiple expressions or multiple function calls ([r206654](https://trac.webkit.org/changeset/206654/), [r206655](https://trac.webkit.org/changeset/206655/)) - Made breakpoints on blank lines or comments break on the next possible line ([r206653](https://trac.webkit.org/changeset/206653/)) - Fixed stepping out of a function so it always takes you to the caller instead of sometimes resuming ([r206652](https://trac.webkit.org/changeset/206652/), [r206693](https://trac.webkit.org/changeset/206693/)) - Fixed stepping to a line in the debugger with an “auto continue” breakpoint so it still pauses ([r206698](https://trac.webkit.org/changeset/206698/)) - Fixed refreshing while in the Timelines tab would cause negative timestamps in the Network tab ([r206464](https://trac.webkit.org/changeset/206464/)) - Fixed a bug where Box Model values were not updated when DOM node styles changed ([r206406](https://trac.webkit.org/changeset/206406/)) - Fixed a bug where the DOM would not update when editing Box Model values (border, margin, etc.) ([r206363](https://trac.webkit.org/changeset/206363/)) - Added a console message when an anchor `download` attribute is ignored ([r206562](https://trac.webkit.org/changeset/206562/)) - Made clicking a second time on the color swatch square hide the CSS color picker ([r206729](https://trac.webkit.org/changeset/206729/)) ### Media - Fixed Picture in Picture playback so it always shows the correct state of the play button ([r206520](https://trac.webkit.org/changeset/206520/)) ### Accessibility - Exposed a `label` element’s text content as the description for `meter` elements ([r206581](https://trac.webkit.org/changeset/206581/)) - Exposed a `label` element’s text content as the description for `progress` elements ([r206391](https://trac.webkit.org/changeset/206391/)) ### URL Handling - Navigations to `tel:` and `mailto:` links now require a user gesture; navigations without a user gesture will show a confirmation prompt - Users are now prompted when navigating to URLs that open other applications ### Security - Fixed an issue where a CSP violation report may be sent to the wrong domain when the `frame-ancestors` directive is violated ([r206278](https://trac.webkit.org/changeset/206278/)) ### Safari Extensions - Fixed an issue where Safari Technology Preview would consume excess memory when certain Safari Extensions were installed ([r206885](https://trac.webkit.org/changeset/206885)) --- Copyright © 2026 Apple Inc. 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