Can anyone explain how affinity labels work in 4.4?

I created a label containing a host and a VM. I had assumed that would require the VM to run on that host, but the VM continues to run on any host in the cluster.

I then checked the 4.4 documentation and it says that I need the filters module section of scheduling policy to contain Label, but there's doesn't appear to be a filter called Label.

Am I missing something?