The format appears to have changed slightly for the upcoming 22.03 release, the rules now look like this:
config match
option networkid 'bios'
option match '60,PXEClient:Arch:00000'
I added this syslinux based example to the wiki as it was very useful, and under-documented as you say. If you want to add another working one for iPXE I'm sure many would find it handy 