David Rector wrote:
> Do I understand correctly that this means the user does not *ever* need to
> directly use the double-underscored keywords —

In C++, identifiers containing double underscore are reserved for the
implementation (http://eel.is/c++draft/lex.name#3). These are generally
never used by the standard. C standards have had a practice of using these
reserved identifiers (e.g. _Bool), but this is not the case in C++.

I don't think a standard C++ keyword will ever be double-underscored.