blocks|key|1056862|text|XML解析器只需要支持至少UTF-8和UTF-16。XML解析器首先尝试基于Byte+Order+Mark+(BOM)的编码，如果存在的话(对于UTF-16，UTF-32，甚至UTF-8和虚拟BOM)。如果没有找到，则解析器将尝试UTF-32、UTF-16、UTF-8、ASCII和其他与ASCII兼容的单字节编码。只有这样，它才会看到编码属性，并在必要时重新启动解析。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1056863|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

XML parsers are only required to support at least UTF-8 and UTF-16. The XML parser starts by trying the encodings based on the Byte Order Mark (BOM), if present (for UTF-16, UTF-32 and even UTF-8 with the dummy BOM). If none is found, then the parser will try UTF-32, UTF-16, UTF-8, ASCII and other ASCII-compatible single-byte encodings. Only then will it see the encoding attribute, and will restart parsing if necessary.

blocks|key|1056878|text|我认为原则上您可能有一点认为encoding语句在文件中是‘迟’的，但是整个第一行只使用基本字符。AFAIK，几乎所有的编码都是相同的，所以不管你把它解码为什么，它都会读<?xml+...+?>。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1056879|然而，无论在那之后发生了什么，都可能很重要。例如，CDATA部分中的文本可以用Cyrillic编码编码。|1056880|entityMap^0|E|8|2D|C|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

I think in principle you might have a point that the <code>encoding</code> statement is 'late' in the file, however, the whole first line only uses basic characters. AFAIK, those are the same in almost all encodings, so whatever you decode it as, it'll read <code>&lt;?xml ... ?&gt;</code> anyway.

Whatever comes after that however, could matter. For example text in a CDATA section could be encoded in a Cyrillic encoding.

blocks|key|2254440|text|正如您所提到的，您必须知道文件的编码才能读取encoding属性。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2254441|但是，有一种启发式方法可以很容易地使您接近“真实”编码，从而允许您读取编码属性。这是可行的，因为根据定义，<?xml部件只能包含ASCII范围中的字符(尽管它们是编码的)。|2254442|XML标准甚至是描述用于查找编码的确切过程。。|2254443|编码标签也不是多余的。例如，如果您使用XML规范中的算法来发现使用了一些基于ASCII的(或与ASCII兼容的)编码，则仍然需要读取编码以确定实际使用的编码(有效的候选是ASCII、UTF-8、任何编码、任何*编码、KOI8-R和许多其他编码)。对于<?xml部分本身来说，它不会改变它是哪个部分，但是对于文档的其余部分，它会产生巨大的不同。|2254444|关于错误标记的XML文件:是的，很容易生成这些文件，但是：XML规范明确规定这些文件是不正常的，因此是不正确的。不正确的编码必须报告为错误(只要可以检测到！)。因此，这是生成XML的人的问题。|2254445|entityMap|0|LINK|mutability|MUTABLE|url|http://www.w3.org/TR/REC-xml/#sec-guessing|1|http://en.wikipedia.org/wiki/ISO/IEC_8859|2|http://en.wikipedia.org/wiki/Windows_code_page|3|http://en.wikipedia.org/wiki/KOI8-R^0|M|8|0|1H|5|0|8|E|0|0|3H|5|2R|2|1|2W|1|2|30|6|3|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|17|8|@]|D|@$9|18|A|19|1|1A]]|E|$]]|$1|J|3|K|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@$9|1E|A|1F|1|1G]|$9|1H|A|1I|1|1J]|$9|1K|A|1L|1|1M]]|E|$]]|$1|L|3|M|5|6|7|1N|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1O|8|@]|D|@]|E|$]]]|O|$P|$5|Q|R|S|E|$T|U]]|V|$5|Q|R|S|E|$T|W]]|X|$5|Q|R|S|E|$T|Y]]|Z|$5|Q|R|S|E|$T|10]]]]

As you mentioned, you'd have to know the encoding of the file to read the <code>encoding</code> attribute.

However, there is a heuristic that can easily get you close enough to the "real" encoding to allow you to read the encoding attribute. This works, because the <code>&lt;?xml</code> part by definition can only contain characters in the ASCII range (however they are encoded).

The XML standard even <a href="http://www.w3.org/TR/REC-xml/#sec-guessing" rel="noreferrer">describes the exact process used to find out the encoding</a>.

And the encoding label isn't redundant either. For example, if you use the algorithm in the XML spec to find out that some ASCII-based (or ASCII-compatible) encoding is used you still need to read the encoding to find out which one is actually use (valid candidates would be ASCII, UTF-8, any of the <a href="http://en.wikipedia.org/wiki/ISO/IEC_8859" rel="noreferrer">ISO-8859-* encodings</a>, any of the <a href="http://en.wikipedia.org/wiki/Windows_code_page" rel="noreferrer">Windows-*</a> encodings, <a href="http://en.wikipedia.org/wiki/KOI8-R" rel="noreferrer">KOI8-R</a> and many, many others). For the <code>&lt;?xml</code> part itself it won't make a difference which one it is, but for the rest of the document, it can make a huge difference.

Regarding mis-labeled XML files: yes, it's easy to produce those, however: the XML spec clearly specifies that those files are mal-formed and as such are not correct XML. Incorrect encodings must be reported as an error (as long as they can be detected!). So it's the problem of whoever is producing the XML.

blocks|key|2254458|text|你说得对，这看起来像个奇怪的设计。它只起作用，因为XML声明只使用ASCII字符，而且几乎所有编码都是ASCII的超集。如果您准备接受一些不是的东西，例如EBCDIC，您可以检查文件是否以"<?xml"的EBCDIC表示形式开头。这意味着您所依赖的是文件头中的一般冗余级别，而不是纯粹的编码属性本身。与XML中的许多东西一样，它很实用，也很有效，但并不特别优雅。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2254459|entityMap^0|2M|7|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

You're quite right that it looks like an odd design. It only works because the XML declaration uses only ASCII characters, and nearly all encodings are supersets of ASCII. If you're prepared to accept something that isn't, for example EBCDIC, you can check whether the file starts with whatever the EBCDIC representation of <code>"&lt;?xml"</code> is. Which means you're relying on the general level of redundancy in the header of the file, rather than purely the encoding attribute itself. Like many things in XML, it's pragmatic and works, but isn't particularly elegant.

Looking at the XML header

<pre><code>&lt;?xml version="1.0" encoding="UTF-16" standalone="no"?&gt;
</code></pre>

Am I right to state that the <code>encoding</code> attribute is 

<ul>
<li>coming too late (you can't read it properly unless you know the encoding...)</li>
<li>redundant, hence error-prone: it's all too easy to replace it with "Big5" yet save the file in UTF-8</li>
</ul>

Or is that attribute not about the content of the stream?

Am I mixing up things here?

What use is the 'encoding' in the XML header?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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查看XML头<?xml version="1.0" encoding="UTF-16" standalone="no"?>我是否正确地声明encoding属性是太迟了(除非你知道编码，否则你无法正确地读懂它.)冗余，因此容易出错:用"Big5“替换它太容易了，但是将文件保存在UTF-8中或者，该属性是否与流的内容无关？...

问XML头中的“编码”有什么用？
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问XML头中的“编码”有什么用？EN