There are four configuration files that enable personal preferences to
be incorporated into the LaTeX format file latex.fmt. The range
of preferences that can be configured by these files is strictly
limited as this helps to ensure document portability.
All four files work in the same way: if the file <file>.cfg is
found, it will be input by iniTeX; otherwise a default file
<file>.ltx will be input instead. Thus, providing one of these
.cfg files completely overrides any settings in the corresponding
standard .ltx file.