The event and first-input performance entries and the PerformanceEventTiming API measures the latency of user input events, such as mouse clicks or keypresses. They're used to calculate Interaction to Next Paint (INP), a common metric for perceived responsiveness.

The command and commandfor attributes for the <button> HTML element dispatch an action to an element when the button is invoked (by click or keystroke), as a declarative alternative to addEventListener() calls or onclick attribute handlers.

The largest-contentful-paint performance entry and the LargestContentfulPaint API measures the time it takes for the largest image or text to appear. Largest contentful paint (LCP) is a common metric for perceived loading times.

The text-decoration-line: spelling-error and text-decoration-line: grammar-error CSS declarations apply the browser's marking for spelling and grammatical mistakes. This is typically a wavy underline in red or green.

The document.caretPositionFromPoint() method finds an insertion point, represented by a DOM node and an offset within that node, for given coordinates in the viewport.

The scrollbar-color CSS property sets the color of the scrollbar track and thumb.

The scrollend event fires when an element or document has finished scrolling.

The Atomics.waitAsync() static method waits for a value in a shared memory location, providing a promise when the expected value is not yet in memory. The waitAsync() method is a non-blocking alternative to Atomics.wait().

View transitions allow you to create animated visual transitions between different states of a document.

The view-transition-class CSS property sets a name that can be used to apply styles to multiple named view transition pseudo-elements.

The WebRTC encoded transform API allows you to modify audio and video streams in WebRTC connections. For example, it can be used for visual effects or custom codecs.

The ::details-content pseudo-element selects the expandable content of a <details> element, excluding the <summary>.

The rel="dns-prefetch" attribute for the <link> HTML element is a hint to the browser that the page or user is likely to request resources from another domain, so the browser should preemptively resolve DNS for the href value's domain.

The URLPattern API creates patterns that can be matched against URLs or URL components.

The Document.parseHTMLUnsafe() static method parses HTML into a DOM tree, while the setHTMLUnsafe() method of Element and ShadowRoot parses and inserts HTML into an existing tree. No sanitization applies to these methods, so never call them with user-provided HTML strings.

The content-visibility CSS property delays rendering an element, including layout and painting, until it is needed.

The static Uint8Array.fromBase64() method and the Uint8Array instance methods toBase64() and setFromBase64() convert to and from base64 strings. Similarly, the static Uint8Array.fromHex() method and the instance methods toHex() and setFromHex() convert to and from hex strings.

The <input type="file" webkitdirectory> HTML element shows a file picker from which users can choose a folder to upload with the form.

The window.getSelection().getComposedRanges() method returns ranges that represent the current user selection, even if the selection spans across shadow tree boundaries.

The abs() and sign() CSS functions compute the absolute value or the sign of the input.

When caught, an exception is reified into an exception reference, a value of the new type exnref.

The requestClose() method of a <dialog> HTML element closes the dialog, firing a cancel event first, which listeners can use to prevent the dialog from closing. This differs from the close() method, which only fires the non-cancelable close event.

The EXT_texture_compression_rgtc extension for WebGL 1.0 and 2.0 contexts adds RGTC compressed texture formats. RGTC is a block-based texture compression format suited for unsigned and signed red and red-green textures. Also known as Red-Green Texture Compression.

The RegExp.escape() static method takes a string and replaces any characters that are potentially special characters of a regular expression with equivalent escape sequences. For example, RegExp.escape("[abc]") returns "\\[abc\\]".

The print-color-adjust CSS property sets whether styles of printed pages should be adjusted to use less ink, in cases such as light text on a dark background.

Module import … with { type: "json" } statements load JSON data. Also known as JSON module scripts.

Float16Array is a typed array of 16-bit floating point numbers.

The Atomics.pause() static method gives a hint to the CPU that the code calling the method is in a short-duration wait for shared memory, known as spinning or a spinlock.

The ClipboardItem.supports() static method checks if the browser supports writing data types such as "image/svg+xml" or other custom formats to the system clipboard.

The Iterator object is an abstract base for objects that implement the iterator protocol. It provides methods common to built-in iterators, such as filter(), find(), map(), and reduce(). You can also use the static method Iterator.from() to convert an existing iterable into an Iterator.