url编码和utf8区别「带BOM的UTF-8」和「⽆BOM的UTF-8」有什么区别？
UTF-8 不需要 BOM，尽管 Unicode 标准允许在 UTF-8 中使⽤ BOM。
所以不含 BOM 的 UTF-8 才是标准形式，在 UTF-8 ⽂件中放置 BOM 主要是微软的习惯（顺便提⼀下：把带有 BOM 的⼩端序 UTF-16 称作「Unicode」⽽⼜不详细说明，这也是微软的习惯）。
BOM（byte order mark）是为 UTF-16 和 UTF-32 准备的，⽤于标记字节序（byte order）。微软在 UTF-8 中使⽤ BOM 是因为这样可以把 UTF-8 和 ASCII 等编码明确区分开，但这样的⽂件在 Windows 之外的操作系统⾥会带来问题。
「UTF-8」和「带 BOM 的 UTF-8」的区别就是有没有 BOM。即⽂件开头有没有 U+FEFF。
UTF-8 的⽹页代码不应使⽤ BOM，否则常常会出错。这是⼀个⼩例⼦：为什么这个⽹页代码 <head> 内的信息会被浏览器理解为在 <body>内？
另附《The Unicode Standard, Version 6.0》之 3.10 D95 UTF-8 encoding scheme 的⼀段话：
While there is obviously no need for a byte order signature when using UTF-8, there are occasions when processes convert UTF-16 or UTF-32 data containing a byte order mark into UTF-8. When repre
sented in UTF-8, the byte order mark turns into the byte sequence. Its usage at the beginning of a UTF-8 data stream is neither required nor recommended by the Unicode Standard, but its presence does not affect conformance to the UTF-8 encoding scheme. Identification of the byte sequence at the beginning of a data stream can, however, be taken as a near-certain indication that the data stream is using the UTF-8 encoding scheme.

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