protected override Boolean IsValid(CSSValue value) { VerticalAlignMode mode; var calc = value.AsCalc(); if (calc != null) { _mode = new CalcVerticalAlignMode(calc); } else if (value is CSSIdentifierValue && modes.TryGetValue(((CSSIdentifierValue)value).Value, out mode)) { _mode = mode; } else if (value != CSSValue.Inherit) { return(false); } return(true); }