SNORT keywork to check TCP window size

["Alberto Grazi" <grazi_alberto () hotmail com>]

Hi, 
does anyone know how to check the window size of a TCP packet in a SNORT
rule? 
I've been looking in the documentation and on the Net but I haven't
found it yet... there has to be a way, it's written in the changelog!

Any help is appreciated.
Regards
Alberto Grazi