wb(from rgb(20%, 40%, 60%, 80%) h w 20% / alpha)`, `rgba(51, 128, 204, 0.8)`);
    test_valid_value(`color`, `hwb(from rgb(20%, 40%, 60%, 80%) h w b / .2)`, `rgba(51, 102, 153, 0.2)`);

    // Testing valid permutation (types match).
    test_valid_value(`color`, `hwb(from rebeccapurple h b w)`, `rgb(153, 102, 204)`);
    test_valid_value(`color`, `hwb(from rebeccapurple h alpha w / b)`, `rgba(213, 213, 213, 0.4)`);
    test_valid_value(`color`, `hwb(from rebeccapurple h w w / w)`, `rgba(128, 51, 204, 0.2)`