Menuentry for Archlinux under Grub

It may not sound llike a FreeBSD question, but it is really...

I'm trying to add Archlinux to my grub based Multiboot disk which has been partitioned with gpart. I have added various Linux distros already, but am having problems figuring out the entry for Archlinux... I read a guide here:-

but this is full of Linuxisms.... In particular I don't know how to interpret this:-

As it is recommend to use a persistent name instead of /dev/sdxY to identify the partition on the USB drive where the image files are located, define a variable for convenience to hold the value. If the ISO images are on the same partition as grub, use the following to read the UUID at boot time:

# path to the partition holding ISO images (using UUID)
probe -u $root --set=rootuuid
set imgdevpath="/dev/disk/by-uuid/$rootuuid"
Or specify the UUID explicitly:

# path to the partition holding ISO images (using UUID)
set imgdevpath="/dev/disk/by-uuid/UUID_value"
Alternatively, use the device label instead of UUID:

# path to the partition holding ISO images (using labels)
set imgdevpath="/dev/disk/by-label/label_value"
The necessary UUID or label can be found using lsblk -f. Do not use the same label as the Arch ISO for the USB device, otherwise the boot process will fail.

I have all the ISO images in an FAT32 formatted ms-basic-data partition labelled DOS which is gpt6. How should I specify 'imgdevpath'? /dev/ada0/DOS ?