Graceful shutdown of Bhyve VM?

Hello, I'm using bhyve without any front-ends like the vm-bhyve package 
and whatnot, I was wondering how to properly perform a graceful shutdown 
of a VM without explicitly calling shutdown within it. I know qemu can 
send an ACPI shutdown signal to it, and apparently vm-bhyve can do 
something similar but it isn't clear through what mechanism it does this.

/ Leo