The W3C CSS validator throws Value Error : margin-top Too many values or values are not recognized : 1px \9. It does not complain about 1px\9.
See https://stackoverflow.com/questions/8004765/what-is-the-meaning-of-9-in-this-width-property-value-declaration, https://stackoverflow.com/questions/18907131/detecting-ie-version-using-css-capability-feature-detection, https://www.w3.org/TR/CSS2/syndata.html#characters