Do "byte order marks" fall into the domain of plain text files? If so, how should I consider them? They're usually not visible in a text editor (even vim), whi

Do "byte order marks" fall into the domain of plain text files? If so, how should I consider them? They're usually not visible in a text editor (even vim), which means that simple file concatenation could produce bizarre results if one concatenated a little-endian (UTF-16) with a big-endian file.