Question

Terminates the last protected function called
and returns message as the error message.
Function error never returns.

Usually, error adds some information about the error position
at the beginning of the message.
The level argument specifies how to get the error position.
With level 1 (the default), the error position is where the
error function was called.
Level 2 points the error to where the function
that called error was called; and so on.
Passing a level 0 avoids the addition of error position information
to the message.