alpha)`, `oklch(0.7 0.45 0 / 0.4)`);
    test_valid_value(`color`, `oklch(from oklch(0.7 0.45 30 / 40%) l c h / 0)`, `oklch(0.7 0.45 30 / 0)`);

    // Testing replacement with a constant.
    test_valid_value(`color`, `oklch(from oklch(0.7 0.45 30) 0.25 c h / alpha)`, `oklch(0.25 0.45 30)`);
    test_valid_value(`color`, `oklch(from oklch(0.7 0.45 30) l 0.25 h / alpha)`, `oklch(0.7 0.25 30)`);
    test_valid_value(`color`, `oklch(from oklch(0.7 0.45 30) l c 0.25 / alpha)`, `oklch(0.7 0.45 0.25)`);
    test