What is "S" in CSS grammar?

Hi,

http://www.w3.org/TR/CSS2

The above document mentioned something link this.

hexcolor
: HASH S*
;

I also see the following. I'm wondering if the following S is the above S.

S s|\\0{0,4}(53|73)(\r\n|[ \t\r\n\f])?|\\s

I know some of above syntax, but not all. Could anybody help me
understand what the above sentence mean?

I'm not familiar enough with flex syntax. Sorry for asking a naive question.

-- 
Regards,
Peng