xml - 哪些是 HTML 和 XML 特殊字符？

Question

HTML 和 XML 中的特殊保留字符实体是什么？

我所掌握的信息是这样的:

HTML:

• & (替换为 & )
• < (替换为 < )
• <罢工> > (替换为 > )
• " (替换为 " )
• <罢工> ' (替换为 ' )

XML:

• < (替换为 < )
• > (替换为 > )
• & (替换为 & )
• ' (替换为 ' )
• " (替换为 " )

但我找不到关于这些的文档。

W3C 在 Extensible Markup Language (XML) 1.0 (Fifth Edition) 中确实提到了，某些预定义的实体引用。但它说这些实体是预定义的(与预定义 © 的方式相同)；并不是说它们必须被转义:

4.6 Predefined Entities

[Definition: Entity and character references may both be used to escape the left angle bracket, ampersand, and other delimiters. A set of general entities (amp, lt, gt, apos, quot) is specified for this purpose. Numeric character references may also be used; they are expanded immediately when recognized and must be treated as character data, so the numeric character references " &#60; " and " &#38; " may be used to escape < and & when they occur in character data.]

哪些字符必须转义为HTML中的实体引用？ 哪些字符必须转义为XML中的实体引用？

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更新:

来自 Extensible Markup Language (XML) 1.0 (Fifth Edition) :

2.4 Character Data and Markup

The ampersand character (&) and the left angle bracket (<) must not appear in their literal form, except when used as markup delimiters, or within a comment, a processing instruction, or a CDATA section. If they are needed elsewhere, they must be escaped using either numeric character references or the strings "&" and "<" respectively.

The right angle bracket (>) may be represented using the string ">", and must, for compatibility, be escaped using either ">" or a character reference when it appears in the string "]]>" in content, when that string is not marking the end of a CDATA section.

To allow attribute values to contain both single and double quotes, the apostrophe or single-quote character (') may be represented as "'", and the double-quote character (") as """.

我读前者是这样说的

必须是:

• < ( < ) 必须是
• & ( & ) 必须是

可能，但当显示为 ]]> 时必须

• > ( > ) 必须是，如果显示为 ]]>

还有那个'和 "根本不必转义；除非你想在引用属性中使用引号。

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来自 HTML 4.01 Specification, HTML Document Representation :

5.3.2 Character entity references

Authors wishing to put the "<" character in text should use "<" (ASCII decimal 60) to avoid possible confusion with the beginning of a tag (start tag open delimiter).

Similarly, authors should use ">" (ASCII decimal 62) in text instead of ">" to avoid problems with older user agents that incorrectly perceive this as the end of a tag (tag close delimiter) when it appears in quoted attribute values.

Authors should use "&" (ASCII decimal 38) instead of "&" to avoid confusion with the beginning of a character reference (entity reference open delimiter). Authors should also use "&" in attribute values since character references are allowed within CDATA attribute values.

Some authors use the character entity reference """ to encode instances of the double quote mark (") since that character may be used to delimit attribute values.

HTML 在规则上更加空泛，但听起来我应该:

• <应该与 < 一起
• >应该与 > 一起
• &应该与 & 一起
• "应该与 " 一起

如果"可以是实体引用，我也应该替换 '与 & .

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更新二

来自 HTML5 - A vocabulary and associated APIs for HTML and XHTML :

8.3 Serializing HTML fragments

Escaping a string (for the purposes of the algorithm above) consists of running the following steps:

Replace any occurrence of the "&" character by the string "&".

Replace any occurrences of the U+00A0 NO-BREAK SPACE character by the string " ".

If the algorithm was invoked in the attribute mode, replace any occurrences of the """ character by the string """.

If the algorithm was not invoked in the attribute mode, replace any occurrences of the "<" character by the string "<", and any occurrences of the ">" character by the string ">".

我读作HTML:

• &通过 &总是
• 通过  总是
• "通过 "如果它在属性内
• <通过 <如果它不在属性中(即属性可以包含 < )
• >通过 >如果它不在属性中(即属性可以包含 > )

Answer 1

首先，您要比较 HTML 4.01 specification用 HTML 5 one . HTML5 与 XML 的联系比 HTML 4.01 更紧密(这就是我们拥有 XHTML 的原因)，所以这个答案将坚持 HTML 5 和 XML。

您引用的引用文献在以下几点上都是一致的:

• <应始终用 < 表示当不指示处理指令时
• >应始终用 > 表示当不指示处理指令时
• &应始终用 & 表示
• except 在 <![CDATA[ ]]> 范围内(仅适用于 XML)

我 100% 同意这一点。您绝不希望解析器将文字误认为是指令，因此始终对任何非空格(见下文)字符进行编码是一个不错的主意。好的解析器知道 <![CDATA[ ]]> 中包含的任何内容不是指令，所以这里不需要编码。

实际上，我从不编码 '或 "除非

• 它出现在属性值(XML 或 HTML)中
• 它出现在 XML 标记的文本中。 ( <tag>&quot;Yoinks!&quot;, he said.</tag> )

两个规范也同意这一点。

所以，唯一的争论点是 (空间)。在这两个规范中唯一提到的是在尝试序列化时。如果不是，您应该始终使用文字 (空间)。除非您正在编写自己的解析器，否则我认为不需要进行任何类型的序列化，所以这不是重点。