Byte order marks are wrong and not part of 'clean' 8-bit handling.
All applications and operating systems should assume files WITHOUT a BOM are either ASCII, or the superset there of, UTF-8.
Please remember to say WHY you disagree if you do.
All applications and operating systems should assume files WITHOUT a BOM are either ASCII, or the superset there of, UTF-8.
Please remember to say WHY you disagree if you do.
If you have a file without a BOM, you have to pick one.
As every 8 bit combination is an ASCII character of some kind, you can interpret every UTF-8 character as a combination of ASCII characters. And what you output will be different to what was input (unless you restrict yourself to single byte UTF-9 characters).
Without some other way of indicating the encoding format of a file, a BOM can be a tool to indicate "It's probably encoded using UTF-X".
However, the question "which?" can still apply. There are many encodings that are a superset of ASCII. UTF-8 is a superset of ASCII, but so are ISO-8859-X (for any "X"), Windows-1252, and many others.
When I've had problems in the past with this it's been around windows machines, which love their own encoding formats.
If it's merely ASCII, it doesn't matter. Nearly every charset contains all valid ASCII texts as a strict subset. UTF-7, UTF-16, UTF-32, and EBCDIC are the major counterexamples, and UTF-7 and EBCDIC aren't going to come up unless you're actually expecting them to. (Technically, ISO-2022 charsets can introduce non-ASCII characters without use of high bit characters, since they switch modes using the ASCII ESC character as part of the sequence. In practice, ESC isn't going to come up in most ASCII text and ISO-2022-JP (the only one still in major use) will frequently use 8-bit characters anyways).
The only useful purpose of a BOM is to distinguish between UTF-16LE and UTF-16BE, and even then it's discouraged in favor of actually maintaining labels (or not storing in UTF-16 in the first place). You can detect UTF-8 in practice without a BOM quite easily, and it's only Microsoft who feels obliged to need them.