Byte Order Marks (BOMs)
Besides UTF-8, there are other UTFs (Unicode Transport Format) and in some of them bytes are interpreted differently depending on whether the machine is big-endian (Sun, Apple) or little-endian (Windows and most Linux machines).
For this reason, the Unicode standard specifies that a file may begin with a Byte Order Mark or BOM, which is a sequence of reserved bytes that indicate byte order as well as the type of UTF encoding.
Note however, the UTF-8 standard (by far the most common UTF) is the same for both big-endian and little-endian machines. BOMs are not needed in UTF-8 files. Unfortunately, the UFT-8 standard allows, but does not require, a BOM mark in the beginning of a file. It does not indicate byte order, it just serves to indicate that the encoding is UTF-8 rather than something else.
Some UTF-8 editors insert a BOM while some do not. A Hex editor shows that the UTF-8 BOM consists of three bytes:
0xEF 0xBB 0xBF
During the import process, SDL Contenta removes the header information and therefore, strips out the BOM since it is not needed to properly support UTF-8. SDL Contenta refers to the information in AppData to obtain the appropriate XML declaration during the checkout (export) process.