Oracle datafile extension .dat or .dbf

Question

I have seen these 2 extensions used for datafiles, .dat and .dbf while creating and/or altering a tablespace. I'm not sure what the difference between the 2 extensions is, or if .dat is incorrect.

Here are 2 examples from Oracle Database SQL Reference 10g Release 2 (10.2)

.dat

CREATE TABLESPACE tbs_01 
   DATAFILE 'tbs_f2.dat' SIZE 40M 
   ONLINE;

.dbf

CREATE TABLESPACE tbs_03 
   DATAFILE 'tbs_f03.dbf' SIZE 20M
   LOGGING;