The protected audience API facilitates advertisement sales by allowing sites to register users as part of an interest group or to choose which ads appear based on those interest groups, while minimizing the ability of advertisers to track specific members of the interest group. Also known as FLEDGE.

The protocol_handlers web app manifest member registers an installed web app as a handler for a specific protocol. When a user follows a link with the specified protocol, the installed app opens the link.

The @container style() CSS at-rule and if(style()) CSS function queries accept a range syntax, such as >, <, >=, <=, to query for inexact values.

The XRView.camera property provides direct access to pose-synchronized camera images within a WebXR session.

The optional formats.unsanitized parameter of the navigator.clipboard.read() method reads unsanitized text/html data from the system clipboard.

The ReadableStream.from() static method converts an iterable or async iterable object, such as an array or async generator function, into a readable stream.

The referenceTarget property of a ShadowRoot object forwards attributes such as for and aria-labelledby to elements inside a shadow DOM. You can use this to, for example, link a <label> to its <input> even if the <input> is in the shadow DOM of a web component.

The compile() method of RegExp objects recompiles an existing regular expression object using a new pattern and flags.

The RegExp object has several static properties to access the input and results of the most-recent regular expression match.

When using navigator.mediaDevices.getDisplayMedia() to capture a browser tab as a video stream, the region capture API allows you to crop the video to the bounding box of a given element. In contrast to the element capture API, any content that overlays that element is also captured.

The related_applications web app manifest member lists operating system-specific applications that are related to the current web app, such as an Android app that provides similar functionality. The getInstalledRelatedApps() method lists which of those are installed on the current device.

Related website sets declares relationships between sites so the browser allows cookie and storage access between them through methods such as document.requestStorageAccessFor().

Relaxed SIMD (Single Instruction Multiple Data) introduces local non-determinism, where the results of the instructions may vary based on hardware support.

The Remote Playback API initiates and controls playback of media on connected remote devices, such as smart TVs with AirPlay or Chromecast capabilities.

The frame-sizing CSS property sets the size of an <iframe> element to that of it contents, to avoid scrolling in the iframe. Embedded documents allow this with the <meta name="responsive-embedded-sizing"> element and request resizing in the embedding page by calling window.requestResize().

The reversed() CSS function for counter-reset creates a counter that counts down.

The line-height-step CSS property creates consistent vertical rhythm by setting the spacing between body text baselines. It rounds taller lines like headings up to the next multiple of the body text spacing.

The SVG 1.1 image format has several components that were excluded from SVG 2, such as fonts, alternate glyphs, and the xlink namespace.

The image/svg+xml data type (also known as the MIME type) for ClipboardItem objects represents SVG data written to or read from the clipboard.

The Sanitizer API customizes the sanitization of HTML parsed and inserted into the DOM in a way that can prevent cross-site scripting attacks. You can use it with DOM APIs that accept a sanitizer option, such as parseHTML() or setHTML().

Browsers send the Save-Data HTTP request header when the user turns on a data-saving mode. It is a hint to reduce data sent to the browser. Servers should respond with alternative content, such as smaller images and videos, or different markup and styling.

The scheduler API provides a way to prioritize all tasks belonging to an application.

The CustomElementRegistry() constructor creates a new custom element registry that's separate from the global window.customElements registry. Creating more than one registry is useful for multiple custom elements that have the same tag name to coexist.

The navigator.mediaDevices.getDisplayMedia() method asks the user to choose a screen or portion of a screen (such as a window) to capture as a media stream.

The screen.orientation.lock() method prevents changes to the screen orientation, typically in fullscreen applications such as games. For example, while locked, rotating a phone to the side won't change the screen orientation from landscape to portrait.

The :target-current CSS pseudo-class selects the active scroll marker (as in ::scroll-marker), while the :target-after and :target-before pseudo-classes select the inactive markers preceding and following the active scroll marker.

A scroll marker scrolls a container to a scroll target. The ::scroll-marker CSS pseudo-element selects a scroll marker in a ::scroll-marker-group pseudo-element, generated before or after the scroll container. You can use them to navigate and style tables of contents, tab panels, and carousels.

The scroll(), scrollBy(), scrollTo(), and scrollIntoView() methods on the Element and Window interfaces return Promises that resolve when scrolling completes.

The scrollsnapchanging and scrollsnapchange events fire when a scroll gesture changes the selected scroll snap target.

The animation-timeline, scroll-timeline, and view-timeline CSS properties advance animations based on the user's scroll position.