HOME_DIR in apache.fc

Hi all,

I am using targeted policy on FC4. In the apache.fc file, the first line is
HOME_DIR/((www)|(web)|(public_html))(/.+)?
system_u:object_r:httpd_ROLE_content_t

I want to know where "HOME_DIR" is defined?  The "apol" tool did not show 
the definition of HOME_DIR. Btw, is HOME_DIR related to
attribute user_home_dir_type;
attribute home_dir_type;
type user_home_dir_t;

Thanks, 

James