'.
    test_valid_value(`color`, `rgb(from rebeccapurple none none none)`,                         `rgb(0, 0, 0)`);
    test_valid_value(`color`, `rgb(from rebeccapurple none none none / none)`,                  `rgba(0, 0, 0, 0)`);
    test_valid_value(`color`, `rgb(from rebeccapurple r g none)`,                               `rgb(102, 51, 0)`);
    test_valid_value(`color`, `rgb(from rebeccapurple r g none / alpha)`,                       `rgb(102, 51, 0)`);
    test_valid_value(`color`, `rgb(from rebecca