text-shadow

Dear Sirs,

..header_usl {
	font-family: Verdana, Geneva, Arial, Helvetica, sans-serif;
	font-size: 13px;
	font-weight: bold;
	color: #333366;
	text-transform: uppercase;
	text-shadow: 2px 2px 2px #FFCC00;
	line-height: 20px;
	letter-spacing: 3px;
}

URI : http://hansongenes.net/genealogy/genstyle.css
72
..header_usl
Value Error : text-shadow Property text-shadow doesn't exist : 2px  
2px 2px #ffcc00

I used the text-shadow property as defined under REC-CSS2/text.html  
(16.3.2) and it works fine on my page. The above validation error is  
most
perplexing. I did try different color definitions and even isolated  
it into its own rule. Can you please explain why the validator does  
not recognize
this property.

Thank you,

Mark Hanson