In January 2007, a workshop was run introducing FoX. This was iFax: Integrating Fortran and XML, organized by the National Institute for Environmental eScience.
The materials for this workshop included several talks, a set of documentation, and a number of example programs and problem sets to work through. All of these materials are available for download.
These documents describe all publically usable APIs.
If a subroutine or function, or indeed one of its arguments, is not mentioned above, it is not to be considered part of the stable API, even if it is accessible.
The astute developer is reminded that all times the final reference documentation is the source, which is publically available.