# Safari Technology Preview 13 Release Notes
Preview the latest web technology updates including: Fetch API, Custom Elements, JavaScript, Web APIs, Web Inspector, CSS, Rendering, Security, and Plugins.
## Overview
[Safari Technology Preview](https://webkit.org/blog/6017/introducing-safari-technology-preview/) Release 13 is now [available for download](https://webkit.org/downloads/) for both macOS Sierra betas 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 [204876–205519](https://trac.webkit.org/log/?stop_rev=204876&rev=205519&limit=999).
### Fetch API
- Added support for `BufferSource` bodies ([r205115](https://trac.webkit.org/changeset/205115))
- Fixed blob resource handling to raise a network error when the URL is not found ([r205190](https://trac.webkit.org/changeset/205190))
- Set the blob type correctly for an empty body ([r205250](https://trac.webkit.org/changeset/205250))
- Set the blob type from Response/Request `contentType` header ([r205076](https://trac.webkit.org/changeset/205076))
- Made the body mix-in `text()` decode data as UTF–8 ([r205188](https://trac.webkit.org/changeset/205188))
- Ensured response cloning works when data is loading ([r205110](https://trac.webkit.org/changeset/205110))
- Enabled the Fetch API to load the data URL in same-origin mode ([r205265](https://trac.webkit.org/changeset/205265))
- Prevented any body for opaque responses ([r205082](https://trac.webkit.org/changeset/205082))
- Changed `opaqueredirect` responses to have their URL set to the original URL ([r205081](https://trac.webkit.org/changeset/205081))
- Prevented setting `bodyUsed` when request construction fails ([r205253](https://trac.webkit.org/changeset/205253))
- Set Response `bodyUsed` to check for its body-disturbed state ([r205251](https://trac.webkit.org/changeset/205251))
- Changed response cloning to use `structureClone` when teeing a Response stream ([r205117](https://trac.webkit.org/changeset/205117))
- Aligned the internal structure of `ReadableStream` with the specifications ([r205289](https://trac.webkit.org/changeset/205289))
- Aligned `data://` URL behavior of XHR to match specifications ([r205113](https://trac.webkit.org/changeset/205113))
### Custom Elements
- Added adopted callback for custom elements on `appendChild()` ([r205085](https://trac.webkit.org/changeset/205085))
- Enabled reaction callbacks for adopted custom elements ([r205060](https://trac.webkit.org/changeset/205060))
- Updated the semantics of `:defined` to re-align with specification changes ([r205416](https://trac.webkit.org/changeset/205416))
- Added validations for a synchronously constructed custom element ([r205386](https://trac.webkit.org/changeset/205386))
- Added support for the `whenDefined()` method on the `CustomElementRegistry` ([r205315](https://trac.webkit.org/changeset/205315))
- Added a `CustomElementRegistry` check for reentrancy ([r205261](https://trac.webkit.org/changeset/205261))
### JavaScript
- Enabled assignments in `for…in` head in non-strict mode ([r204895](https://trac.webkit.org/changeset/204895))
- Changed `newPromiseCapabilities` to check that the given argument is a constructor ([r205027](https://trac.webkit.org/changeset/205027))
- Fixed `toString()` to return the correct tag when called on proxy objects ([r205023](https://trac.webkit.org/changeset/205023))
### Web APIs
- Added event support for `` ([r205269](https://trac.webkit.org/changeset/205269))
- Implemented `x`, `y` and `ScrollToOptions` arguments for `Element.scroll()`, `Element.scrollTo()`, and `Element.scrollBy()` ([r205505](https://trac.webkit.org/changeset/205505))
- Updated `location.toString` to make it enumerable ([r204953](https://trac.webkit.org/changeset/204953))
- Updated `location.toString` in Web Workers to make it enumerable ([r204954](https://trac.webkit.org/changeset/204954))
- Changed `Object.preventExtensions(window)` to throw a `TypeError` exception ([r205404](https://trac.webkit.org/changeset/205404))
- Aligned `coords` and `srcset` attribute parsing with the HTML specification ([r205030](https://trac.webkit.org/changeset/205030), [r205515](https://trac.webkit.org/changeset/205515))
- Added support for `CanvasRenderingContext2D.prototype.resetTransform` ([r204878](https://trac.webkit.org/changeset/204878))
- Aligned cross-origin `Object.getOwnPropertyNames()` with the HTML specification ([r205409](https://trac.webkit.org/changeset/205409))
### Web Inspector
- Added IndexedDB Database, ObjectStore, and Index data to the details sidebar ([r205043](https://trac.webkit.org/changeset/205043))
- Added support for Shift-Command-D (⇧⌘D) to switch to the last used dock configuration ([r205413](https://trac.webkit.org/changeset/205413))
- Added support for Shift-Tab (⇧⇥) to un-indent the selected line ([r204924](https://trac.webkit.org/changeset/204924))
- Changed Command-D (⌘D) to select the next occurrence instead of deleting the line ([r205414](https://trac.webkit.org/changeset/205414))
- Added a visual indicator for shadow content in the DOM tree ([r205322](https://trac.webkit.org/changeset/205322))
- Allowed hiding of CSS variables in the Computed styles panel ([r205518](https://trac.webkit.org/changeset/205518))
- Fixed an issue that prevented using an Undo action in the breakpoint editor ([r205499](https://trac.webkit.org/changeset/205499))
- Prevented the resource content view from showing “CR” characters ([r205517](https://trac.webkit.org/changeset/205517))
- Fixed an issue preventing re-inspecting the page after a Web Inspector process crash ([r205370](https://trac.webkit.org/changeset/205370))
- Improved the minification detection heuristic for small resources ([r205314](https://trac.webkit.org/changeset/205314))
- Fixed an issue causing network record bars to be positioned on unexpected rows ([r205349](https://trac.webkit.org/changeset/205349))
- Provided a way to clear an IndexedDB object store ([r205041](https://trac.webkit.org/changeset/205041))
- Improved the debugger popover to pretty print functions ([r205223](https://trac.webkit.org/changeset/205223))
- Corrected unexpected cursor changes while dragging ruler handle in the rendering frames timeline ([r204940](https://trac.webkit.org/changeset/204940))
- Corrected the display of a plain text XHR response with `responseType="blob"` ([r205268](https://trac.webkit.org/changeset/205268))
### CSS
- Implemented `CSS.escape` according to the CSSOM specification ([r204952](https://trac.webkit.org/changeset/204952))
- Improved CSS stylesheet checks to ensure clean stylesheets are accessible from JavaScript ([r205455](https://trac.webkit.org/changeset/205455))
- Improved `:enabled` and `:disabled` selectors to only match elements that can be disabled ([r205050](https://trac.webkit.org/changeset/205050))
### Rendering
- Fixed scrollbars for a `