Where is the latest document of box-align?

Hi,

box-align can be found in the following document.

http://www.w3.org/TR/2009/WD-css3-flexbox-20090723/

But it can not be found in the latest document.

http://www.w3.org/TR/css3-flexbox/

Is box-align removed from the latest working draft? Or there is some
error in the draft? Or there is something else that I don't
understand? Thanks!

-- 
Regards,
Peng