Are file extensions, such as MP3, AIFF, BFM, XML, etc. abbreviations according to the Nemeth Code? Section 49.b states, “When a letter or sequence of letters does not represent a word or phrase, it must be considered as an abbreviation and must be transcribed according to the rules of this code.” It would seem to me that in some file extensions the letters do represent a word, but not in all. Specifically, I would like to know how to treat MP3, in the phrase “Jenny’s MP3 player cost $125.