This is Linux spec, which is UTF-8 based. BOM makes absolutely no sense in UTF-8 world. (Plus "a run of Unicode whitespace" is a very heavy-weight thing, as it

This is Linux spec, which is UTF-8 based. BOM makes absolutely no sense in UTF-8 world. (Plus "a run of Unicode whitespace" is a very heavy-weight thing, as it requires full Unicode database and Unicode parsers. It is pretty likely that apps which might care about cachedir tag will not have this linked in by default.)