Octal notation is traditionally used in several contexts - file mode probably being the most common. If you were writing a JSON object to describe a file to be created, and you were under the mistaken impression that JSON supported octal with a leading zero (like most languages), it would be entirely reasonable to write something like:
Error messages are "blaming the user".. its job is to help inform the user the mistake he made.
You can silently beat your child everytime he makes a mistake, until he accidentally does the job correctly (and doesn't get beaten), but it seems to me that making use of our ability to communicate can be much more efficient (and significantly less painful for the child).
And json is merely a (very innefficient, and somewhat problematic) protocol for information exchange; it's not something you should expect people to have read the spec for, especially when its whole popularity stems from it being "intuitive" -- that is, you don't really need to read the spec to deal with it effectively
https://developer.mozilla.org/Web/JavaScript/Reference/Error...
See for yourself: