Thanks for the info!
No problem. The little yellow box off to the side is a note attached to the same text. You can do either, both, or neither, it seems.
To be fair, I didn’t know this was possible myself until I looked it up, but it seemed silly not to include the functionality, given that the devices have internal storage. I’ve used a similar reader in the past on my desktop (Zinio), and I could at least add notes, if not necessarily highlight text (though I didn;t try the latter).