image-set property is reported as an error... incorrectly

[KevinGIRAULT]

Hello,

The image-set property is not recognized by w3c Jigsaw validator. Here is an example from MDN image-set page:

.box {
  background-image: -webkit-image-set(
    url("small-balloons.jpg") 1x,
    url("large-balloons.jpg") 2x);
  background-image: image-set(
    url("small-balloons.jpg") 1x,
    url("large-balloons.jpg") 2x);
}

The validator seems to recognize only the -webkit version.

Source : https://developer.mozilla.org/en-US/docs/Web/CSS/image/image-set