color`, `rgb(from rgb(20%, 40%, 60%, 80%) alpha alpha alpha / alpha)`, `rgba(204, 204, 204, 0.8)`);

    // Testing mixes of number and percentage. (These would not be allowed in the non-relative syntax).
    test_valid_value(`color`, `rgb(from rebeccapurple r 20% 10)`, `rgb(102, 51, 10)`);
    test_valid_value(`color`, `rgb(from rebeccapurple r 10 20%)`, `rgb(102, 10, 51)`);
    test_valid_value(`color`, `rgb(from rebeccapurple 0% 10 10)`, `rgb(0, 10, 10)`);
    test_valid_value(`color`, `rgb(from rgb(20%,