CSS mask, and related properties such as mask-image, mask-mode, etc, are used to hide an element (partially or fully) by masking or clipping the image at specific points. This feature unprefixes the -webkit-mask* properties and brings them up to spec. This includes mask-image, mask-mode, mask-repeat, mask-position, mask-clip, mask-origin, mask-size, and mask-composite, as well as the "mask" shorthand. Local mask-image references are supported, serialization now matches the spec, and accepted values now match the spec (for example, "add" instead of "source-over" for mask-composite).