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; this is sometimes done via a
minimal <file>.cfg that simply inputs <file>.ltx. Thus,
providing your own version of any of these .cfg files can completely
override any settings in the corresponding default standard .ltx
file.