There are ID3 tags used for MP3 and other files. Old players may not know about them and may misread their data as MPEG frames. To prevent this a tag may break up sequences of 00 bytes with an FF byte. Or may not, because now most players are aware of tags. So there is a preference, at two levels, default and for a single tag. Not too hard to program, but rather unfriendly to a grammar-based approach.

(Another example are checksums.)