What does "exposition only" mean? Why use it?

Question

All over boost.org and also at other sites on the web I've seen code of this form:

class whatever
{
...
   private:
      std::vector<std::string> m_name;  // exposition only
};

What is the meaning of "exposition only"? What is the comment's purpose? What is it trying to tell me?

Answer 1

It's used to indicate one possible way to implement the particular item, but not necessarily the best or recommended way.

Answer 2

One of the definitions of "exposition" is:

the act of expounding, setting forth, or explaining

So I think they are saying that the private member (or whatever) is only shown to help you understand how the API might work ... and that is not formally part of the Boost API.