private void CheckDateTime()
{
CheckNoPrecision();
if (!DateTimeConv.IsValid(_conversion))
throw new UnknownFormatConversionException("t" + _conversion);
CheckBadFlags(FormatFlags.Alternate| FormatFlags.Plus| FormatFlags.LeadingSpace| FormatFlags.ZeroPad| FormatFlags.Group| FormatFlags.Parentheses);
CheckLeftJustifyWidth();
}