Lower-casing the library

[Sylvain Sauvage]

If you mean

All files in the LDraw Parts Library are required to carry the .DAT extension.

then I think this is a typo, because later in the same article it uses .dat

The 512 article says just above the .DAT (my emphasis):

While both upper and lower case letters are permitted in filenames, filenames are case-insensitive. Currently, all official parts are issued with upper-case only names.