-400 / -500%) l a b / alpha)`, `lab(0 -300 -400 / 0)`);

    // Test nesting relative colors.
    test_valid_value(`color`, `lab(from lab(from lab(25 20 50) l a b) l a b)`, `lab(25 20 50)`);

    // Testing non-lab origin to see conversion.
    test_valid_value(`color`, `lab(from color(display-p3 0 0 0) l a b / alpha)`, `lab(0 0 0)`);

    // Testing replacement with 0.
    test_valid_value(`color`, `lab(from lab(25 20 50) 0 0 0)`, `lab(0 0 0)`);
    test_valid_value(`color`, `lab(from lab(25 20 50) 0 0 0 /