Running NMC in the corner?

[Wade Lippman]

I have to extend a circuit 15' for a new outlet. I can run it though holes in the joists, but can also run it in the corner between the ceiling and the walls. I don't see where code allows that, but both of my houses have done it, so I assume it must be okay. What is allowed/restricted? (I know I can use running boards, but that would be ugly.)

I posted this question on a DIY forum and didn't get any meaningful answers!