No. You must use it only in continuous lengths [400.9].
Yes. But only for repair purposes, and that repair must meet the criteria spelled out in 400.9.
It prevents tension from being transmitted to joints or terminals [400.10]. If you see there is tension, then the fitting and cord are not installed properly.
- Yes. You are limited to certain Types. The list is really long, though. It's in 400.11.
- The flexible cord must be at least 18AWG [400.13].