BOM（字节顺序标记）

放置在文本文件开头的字符（U+FEFF），用于指示UTF-16/UTF-32编码中的字节顺序（字节序）。

The BOM is a special Unicode character used to signal the byte order of a text stream. In UTF-16, it distinguishes between little-endian (FF FE) and big-endian (FE FF) formats.

In UTF-8, a BOM (EF BB BF) is sometimes added but is not recommended — it can cause issues with scripts, JSON parsing, and Unix tools that don't expect it. Many text editors add a UTF-8 BOM by default, which can lead to subtle bugs.

Modern best practice: use UTF-8 without BOM for web content and data files.