extern Configuration *_config

APT instantiates the global pointer $\texttt{*\_config}$ for the $\texttt{Configuration}$ class. This class provides a configuration file and a command line parser for a tree-oriented configuration environment. The whole runtime configuration is stored in here. Each option is given as a fully scoped string such as $\texttt{Foo::Bar}$, and associates a text string with it. The $\texttt{Configuration}$ class only provides storage and lookup for this tree, other classes provide configuration file formats (and parsers/emitters if needed). We can retrieve most settings with $\texttt{\_config->Find(''Foo::Bar'')}$.