The configuration system is heavily based on python's module system. The configuration files are standard pybliographer scripts (that is, python code making use of pybliographer extra classes and functions), whose single special feature is to be automatically parsed at startup.
The first file to be parsed is ${prefix}/share/pybliographer/pybrc.py. It defines the most basic characteristics of the system:
structure of the bibliographies being parsed (an article can contain an author, a title, ...)
site wide specific features (use of some non standard fields)
available input and output formats
several format and front-end specific features
This file in turn usually indicates a configuration directory. All the files in this directory are parsed (in alphabetical order). This mechanism allows more flexibility to add new formats: the new format can be installed with a default configuration without messing with the global configuration file.
Finally, if the user provides a file called .pybrc.py in its home directory, this file is then parsed. Of course it can also define a private configuration directory, and override what has been defined before.