CSS3 background animation suggestions

I suggest change behaviour in CSS3 animations.

@keyframes something {
  0% { background-index: 0; background-position; 0px 0px; }
  100% { background-index: 0; background-position; 100px 0px; }
}

#element {
  background: "one", "two"...
  animation: ... something...
}

In result should change background only by zero index. Also few animations
can be combined.
*background-index* - should be CSS3 animation only feature.