Unknown pseudo-element or pseudo-class :nth-child

Hi all,
	
Using
http://qa-dev.w3.org:8001/css-validator/validator
Or
http://jigsaw.w3.org/css-validator/validator

  this css http://xmsi.com/temp.css

body  {
margin : 0 0 0 0;
padding : 0 0 0 0;
}

tr:nth-child(odd) {
     background-color: #ddddff;
     color:inherit
}

tr:nth-child(2n+1) {
     background-color: #ddddff;
     color:inherit
}


and choosing to use CSS3 I get these errors

Unknown pseudo-element or pseudo-class :nth-child
Unrecognized  2n+1)

I think it's valid based on
http://www.w3.org/TR/css3-selectors/#nth-child-pseudo

Is this a bug or am I doing something stupid?

Bob Stuart
RobertStuart@crystalMatrixSoftware.com