http://www.w3.org/TR/css3-transitions/#transition-property-property says : none | [ all | <IDENT> ] [ ‘,’ [ all | <IDENT> ] ]* so it is possible to have "background, font-size, all" as a value. I'm not sure what should be the behavior here : animating all the properties with the last index in the lists of "transition-duration", "transition-delay", ... or animating background, font-size with their respective indices in the lists of "transition-duration", "transition-delay", ... and animating all the other properties with the last index in the lists of "transition-duration", "transition-delay", ... In the other hand "background, font-size, all" goes in conflict with "Otherwise, a list of properties to be transitioned, or the keyword ‘all’ which indicates that all properties are to be transitioned, is given." which seem to assume that all comes alone. Side note : Opera reject this value.