to_iso_extended_string documentation wrong about fraction print

I am using `std::string to_iso_extended_string(ptime)` and have reports that on some system it prints without the second fractions. Consulting the documentation and the header of boost 1.71 I was confronted with inconsistent documentation:

[The Docs are saying it prints with fractions of a second:](https://www.boost.org/doc/libs/1_71_0/doc/html/date_time/posix_time.html)

> std::string to_iso_extended_string(ptime)
> Convert to form YYYY-MM-DDTHH:MM:SS,fffffffff where T is the date-time separator
> 2002-01-31T10:00:01,123456789

[While the accoding header says:](https://github.com/boostorg/date_time/blob/boost-1.71.0/include/boost/date_time/posix_time/time_formatters.hpp#L240)

> //! Convert to form YYYY-MM-DDTHH:MM:SS where T is the date-time separator
> /*!\ingroup time_format
> */
> inline std::string to_iso_extended_string(ptime t){

So YYYY-MM-DDTHH:MM:SS,fffffffff or YYYY-MM-DDTHH:MM:SS, who is right?