CSS3 Border-radius (rounded corners)

Method of making the border corners round. Covers support for the shorthand `border-radius` as well as the long-hand properties (e.g. `border-top-left-radius`)

IntersectionObserver V2

Iteration on the original API that also reports if the element is covered by another element or has filters applied to it. Useful for blocking clickjacking attempts or tracking ad exposure.

KeyboardEvent.key

A `KeyboardEvent` property whose value is a string identifying the key that was pressed. Covers character keys, non-character keys (e.g. arrow keys), and dead keys.

CSS3 object-fit/object-position

Method of specifying how an object (image or video) should fit inside its box. object-fit options include "contain" (fit according to aspect ratio), "fill" (stretches object to fill) and "cover" (overflows box but maintains ratio), where object-position allows the object to be repositioned like background-image does.

CSS outline properties

The CSS outline properties draw a border around an element that does not affect layout, making it ideal for highlighting. This covers the `outline` shorthand, as well as `outline-width`, `outline-style`, `outline-color` and `outline-offset`.

requestAnimationFrame

API allowing a more efficient way of running script-based animation, compared to traditional methods using timeouts. Also covers support for `cancelAnimationFrame`

requestIdleCallback

API allowing the execution of JavaScript to be queued to run in idle browser time, either at the end of a frame or when the user is inactive. Also covers support for `cancelIdleCallback`. The API has similarities with `requestAnimationFrame`.

idbrequest api: error: transient and unrecoverable read errors

webgl2renderingcontext api: samplecoverage

webglrenderingcontext api: samplecoverage

css property: background-size: cover

css property: object-fit: cover

headers http header: access-control-allow-headers: `authorization` header is not covered by wildcard