who knows more details about "Variables Expansion"

[weller]

I don't know how to use "Variables Expansion" in kickstart files, anybody can provide the documents or examples?
such as:
my server IP is: 192.168.149.1
How is it associated with "VT_SERVER_IP"
and,
VT_IMG_PMD5_HTTP_URL，How does it relate to my ISO's PMD5, c413Abe3D9e9c7C5f50e33F6ebX40F68
thanks a lot!