There are four configuration files to control personal preferences that may be incorporated into the LATEX format file, |latex.fmt|. The range of preferences that can be configured by these files is strictly limited 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.