In a peculiarity of Facebook, you can add a message to the person you ask to be your friend …

Time to ponder some technological mysteries, none very significant. In fact, they’re more like curiosities.

1. It remains impossible — so far as I can tell from official Mac and Windows help sites — to send a document from a computer to a fax machine unless the sender connects an analog phone line. We’re trained these days to think wirelessly and digitally; land lines are dwindling as more people use mobile phones as their only phones; our laptops can create PDFs and e-mail them; but you can’t send a file to a fax machine without stepping back a decade?

2. If you have a mobile phone, you may also have a hands-free Bluetooth headset. If you have a laptop with iTunes or some other music player, you probably also have headphones you use to listen to that music. And your laptop is likely to be Bluetooth enabled. So can you use your phone headset to listen to music wirelessly from your laptop — not bothering co-workers and keeping an ear free for, you know, your job? No, not according to computer retail salespeople, even though it seems simple for the industry create a headphone that can take a signal from your computer and mute the sound when a call comes in.

… but you can't send a message back as you accept or reject a Facebook friendship.

3. There was a time when Facebook users could, first, ask someone to be their friend or send a personal message and, second, accept online friendship or send a personal message. Now you can ask someone’s friendship and simultaneously send a personal message. But when that request comes in, you can’t accept (or reject) and accompany it with a personal message (“Hi!” or “Go to hell!”). Isn’t that kind of an obvious one, and one that might have been fixed when the friend-request message was added?