More beginner questions

[Bill MacAllister]

I have a minimal FAI server up to the point where it will install stretch 
on a client system.  I now need to be able to install other distributions. 
I understand that I need to create or download basefiles.  That is straight 
forward to me. What I am fuzzy on is how I create a PXE configuration so 
that the client picks the correct base file.

For example, for a client system I have a PXE config of:

serial 1 9600 0
default fai-generated

label fai-generated
kernel vmlinuz-4.9.0-1-amd64
append initrd=initrd.img-4.9.0-1-amd64 ip=dhcp  
root=172.21.65.51:/srv/fai/nfsroot rootovl console=tty0 
console=ttyS0,9600n8 FAI_FLAGS=verbose,sshd,createvt 
FAI_CONFIG_SRC=nfs://corpfai.corp.dropbox.com/srv/fai/config 
FAI_ACTION=install

How do I tell FAI to add the class XENIAL?

Bill