Did I Forget to Mention This?
The selection property will contain references to tracks selected in Apple Music. You can get properties of these URL tracks, but you can't set them. That would be dumb*.
I neglected to note this earlier because I was falling all over myself about current track and current playlist also being able to reference Apple Music items.
{UPDATE: *I stand corrected. You can set the loved property of the tracks in a selection of Apple Music tracks.]