)`,                               `lch(0.7 45 30 / none)`);
    // FIXME: Clarify with spec editors if 'none' should pass through to the constants.
    test_valid_value(`color`, `lch(from lch(none none none) l c h)`,                                       `lch(0 0 0)`);
    test_valid_value(`color`, `lch(from lch(none none none / none) l c h / alpha)`,                        `lch(0 0 0 / 0)`);
    test_valid_value(`color`, `lch(from lch(0.7 none 30) l c h)`,                                          `lch(0.7 