The contain: paint CSS declaration prevents an element's descendants from being drawn outside the boundaries of the containing element, with any overflow clipped. This permits the browser to avoid slower painting calculations.

The contain: size CSS declaration sets an element's dimensions exclusively by its height and width properties, ignoring its contents and descendants. This permits the browser to avoid slower layout calculations.

The at() method of strings returns the character (one UTF-16 code unit) at an index, including negative indices for getting the character relative to the end of the string. Also known as the relative indexing method.

The appearance CSS property controls the appearance of form controls. Using appearance: none disables any default native appearance and allows the elements to be styled with CSS.

The contain CSS property sets limits to the scope of styles, layout, and paint rendering for speed and efficiency. The none keyword value disables containment, strict is equivalent to contain: size layout style paint, and content is equivalent to contain: layout style paint.

The navigator.hardwareConcurrency property is the number of logical processors available to run threads on the user's computer.

The scroll-behavior CSS property controls whether scrolling is smooth or snaps, for scroll actions not performed by the user such as those triggered by navigation.

The structuredClone() global method creates a deep copy of an object. Values that cannot be cloned can instead be transferred, making the original value no longer usable.

The text-combine-upright CSS property displays multiple characters in the space of a single character in vertical text. This is used in East Asian documents to display Latin-based strings such as components of a date or letters of an initialism.

The text-decoration-skip-ink CSS property sets whether underlines and overlines may be interrupted where the line would cross a glyph.

The text-emphasis CSS property sets position and style for text emphasis marks, especially for East Asian languages.

The color-scheme CSS property sets which color schemes (light or dark) an element uses and may prevent automatic dark mode adjustments by the browser.

The font-synthesis CSS shorthand property disables all font synthesis except the given kinds. To disable a specific kind of font synthesis, instead use the longhand properties such as font-synthesis-style and font-synthesis-weight.

The SharedArrayBuffer object represents bytes shared between multiple workers and the main thread. The Atomics object safely accesses SharedArrayBuffer data to make sure predictable values are read and written and that operations are not interrupted.

Threads in WebAssembly run code in parallel, while atomic memory instructions can guarantee that no two threads can read or write to shared memory at the same time.

The inputmode global HTML attribute gives a hint about what type of data is to be entered into an <input> element, such as text, numeric, or email, so the browser may help the user enter data using an adapted input mechanism, such as an on-screen virtual keyboard.

The externref type can be both a value type and a table element type, while funcref can be a value type.

The enterkeyhint global HTML attribute sets the label for a virtual keyboard's Enter key. For example, enterkeyhint="search" may label the key with a magnifying glass icon.

The fit-content CSS keyword expands a box as needed to fit its contents until the maximum size is reached, preserving the content's preferred aspect ratio.

Bulk memory operations, such as copy and init, mirror the efficiency of native memcpy and memmove operations.

A navigation performance entry measures navigation events, such as loading time or the number of redirects.

Saturating floating-point to integer conversion operators return the maximum or minimum integer value on overflow instead of trapping.

The <input type="date"> and <input type="time"> HTML elements show date and time pickers.

The image-rendering CSS property sets how images are scaled, retaining smoothness for photos, or hard edges for pixel art and QR codes.

The BigInt64Array and BigUint64Array typed arrays represent 64-bit integers, signed and unsigned respectively.

The EXT_color_buffer_float extension for WebGL 2.0 contexts adds color-renderable floating point formats to renderbufferStorage().

The cause property of errors records the specific original cause of the error, particularly for errors that have been re-thrown.

The IndexedDB API is a local storage transactional object database.

CSS logical properties control borders, size, margin, and padding with directions and dimensions relative to the writing mode. For example, in a left to right, top to bottom writing mode, block-end refers to the bottom. Also known as flow relative.

The Referrer-Policy HTTP header and referrerpolicy HTML attributes control whether requests have the Referer header and what information the header contains.