PS - John: the Unicode BOM is about byte order, not bit order. Is it more useful in 16 bit Unicode where every character is two bytes and the BOM says whether the high byte or low byte comes first in each pair.

In UTF-8... well, see Wikipedia - there's no point in my repeating it all here. But that article does show what a BOM looks like to software that's not execting it, and it matches what's showing on Mudcat.