I would like to use
#foo > .bar
animation-duration:calc(inherit + 2s); /* =12s */
inherit keyword can only exist alone as a value in a property declaration. It cannot be used with anything else as a value, because it's a value in and of itself. This means it cannot be used with functions like
calc() either. See CSS2.1 and css3-cascade.
calc() function itself only takes literal numeric values such as numbers, dimensions and percentages.
So to put it simply, the spec doesn't allow using
inherit that way.