one) h s l / alpha)`,             `rgba(102, 153, 102, 0)`);
    test_valid_value(`color`, `hsl(from hsl(none 20% 50% / .5) h s l / alpha)`,                 `rgba(153, 102, 102, 0.5)`);

    // hwb(from ...)

    // Testing no modifications.
    test_valid_value(`color`, `hwb(from rebeccapurple h w b)`, `rgb(102, 51, 153)`);
    test_valid_value(`color`, `hwb(from rebeccapurple h w b / alpha)`, `rgb(102, 51, 153)`);
    test_valid_value(`color`, `hwb(from rgb(20%, 40%, 60%, 80%) h w b / alpha)`, `rgba(51, 1