BOM（Byte Order Mark），字节顺序标记，出现在文本文件头部，Unicode编码标准中用于标识文件是采用哪种格式的编码，但它对于文件的读者来说是不可见字符。
下表列出不同的字符编码的BOM 编码 BOM (十六进制) BOM (十进制) CP1252 字符 UTF-8[t 1] EF BB BF 239 187 191  UTF-16 (BE) FE FF 254 255 þÿ UTF-16 (LE) FF FE 255 254 ÿþ UTF-32 (BE) 00 00 FE FF 0 0 254 255 ␀␀þÿ (␀ refers to the ASCII null character) UTF-32 (LE) FF FE 00 00 255 254 0 0 ÿþ␀␀ (␀ refers to the ASCII null character) UTF-7[t 1] 2B 2F 76 38 2B 2F 76 39 2B 2F 76 2B 2B 2F 76 2F[t 2] 2B 2F 76 38 2D[t 3] 43 47 118 56 43 47 118 57 43 47 118 43 43 47 118 47 43 47 118 56 45 +/v8 +/v9 +/v+ +/v/ +/v8- UTF-1[t 1] F7 64 4C 247 100 76 ÷dL UTF-EBCDIC[t 1] DD 73 66 73 221 115 102 115 Ýsfs SCSU[t 1] 0E FE FF[t 4] 14 254 255 ␎þÿ (␎ represents the ASCII “shift out” character) BOCU-1[t 1] FB EE 28 251 238 40 ûî( GB-18030[t 1] 84 31 95 33 132 49 149 51 „1•3参考：http://en.wikipedia.org/wiki/Byte_order_mark
