image-set() is a CSS type for specifying a range of image options, such as different images for different screen densities, and letting the browser select the best one. It can be used with CSS properties such as background-image. This feature adds the unprefixed "image-set" type so authors no longer need to use "-webkit-image-set". The implementation has also been brought up to the current spec with new resolution units (dppx, dpi, dpcm), image type support (e.g., type("image/avif")), raw urls without "url()", and gradient image options.
Currently Blink only supports '-webkit-' prefixed image-set, while Gecko and WebKit support both prefixed and unprefixed versions. With this change interop with Gecko and WebKit will be increased by allowing web developers to use the current Blink image-set functionality both with and without the '-webkit-' prefix.