OK, it’s weird. I thought it had been going black when I close the lid, but it does not. The external display seems to get somewhat brighter/bluer in tone, and I can move the cursor around.
What’s weirder is as soon as I open the lid everything disappears from the external display and is moved to the main display! (I used Display Maid to restore the windows - very convenient app.)
So what does this mean?
Maybe TidBits needs a “Taking Control of Sleep” book. :)