Translucency in CSS2/3: Opacity?

Hi Everyone,
Is there anything equivalent to an "opacity" property in CSS2/3 (for
bacgrounds &/or elements)?
I'm looking to have a kind of translucent background for a block level
element. It's useful if you have a bakground image, and a box over the top,
for example.
I couldn't find anything equivalent to transluency in CSS2...
Any help appreciated,
Kindest Regards,
Sean B. Palmer
----------------------------------------------------
WAP Tech Info - http://www.waptechinfo.com/
Mysterylights.com - http://www.mysterylights.com/
XHTML Modularization Resource - http://xhtml.waptechinfo.com/modularization/
----------------------------------------------------
"The Internet; is that thing still around?" - Homer J. Simpson