t_valid_value(`color`, `hsl(from rebeccapurple h s l / alpha)`, `rgb(102, 51, 153)`);
    test_valid_value(`color`, `hsl(from rgb(20%, 40%, 60%, 80%) h s l / alpha)`, `rgba(51, 102, 153, 0.8)`);
    test_valid_value(`color`, `hsl(from hsl(120deg 20% 50% / .5) h s l / alpha)`, `rgba(102, 153, 102, 0.5)`);

    // Test nesting relative colors.
    test_valid_value(`color`, `hsl(from hsl(from rebeccapurple h s l) h s l)`, `rgb(102, 51, 153)`);

    // Testing non-sRGB origin colors to see gamut mapping.
    te