02, 153, 0.8)`);
    test_valid_value(`color`, `hwb(from hsl(120deg 20% 50% / .5) h w b / alpha)`, `rgba(102, 153, 102, 0.5)`);

    // Test nesting relative colors.
    test_valid_value(`color`, `hwb(from hwb(from rebeccapurple h w b) h w b)`, `rgb(102, 51, 153)`);

    // Testing non-sRGB origin colors to see gamut mapping.
    test_valid_value(`color`, `hwb(from color(display-p3 0 1 0) h w b / alpha)`, `rgb(0, 249, 66)`); // Naive clip based mapping would give rgb(0, 255, 0).
    test_valid_value(`color`