Thank you for your reply. They are indeed very vague on their policies.

As I said earlier, I would like to know specifically what are their definitions of the terms "small musical instrument" and "unusual or fragile items". What about other fragile items that cannot be safely checked?

If I have delicate electronic equipment that's used to make music, is it included? What about other electronic equipment that's too delicate to check?

TSA suggests always taking fragile items as carry-on, but I can find nothing in the airline policies that specifically speak to this.