Cue

The CSS   property is a shorthand property for setting both  and   property values. If two values are given, the first value is assigned to  and the second is. Those two values must be separated by a space. If only one value is given, it applies to both properties. If loading of a URL fails, nothing should be played, but if the system does not have the ability to play it, the spec says the system should try to use some sort of cue (audio, visual or other).

Values
HTML example:

TEXT

CSS example:

strong { cue:url(orchestralsneeze.wav) url(quack.wav); }