Manifest - OS Feaures - How and where to define them

I’m currently looking for ways to utilize manifests, such that it is possible to pull specific images on devices with the same os/arch combination.

I just found out about the --os-features argument for the annotate command but I can’t find any information on how or where these features get defined.

I would like to be able to give my devices a specific feature (i.e.: “A”, “B”) and annotate each image with the feature.

Does anyone have more resources/information on this parameter? And is it possible to set the features yourself on the host?