在HTML5中使用null实体（例如&＃x0;）是否有效？ [英] Is the use of the null entity (e.g �) valid in HTML5?
问题描述
我认为 null实体（&＃x0; ）在XML中正式无效。但我在处理HTML时遇到过它。 （也许代表一种零宽度字符？）但它是否有效标记并且浏览器会不会出现？
I believe the null entity (�) is officially invalid in XML. But I have encountered it when processing HTML. (Perhaps to represent a kind of zero-width character?) But is it valid markup and will browsers freak out?
推荐答案
否，它不是有效的HTML5。您可以通过 W3C 验证器运行以下片段来轻松查看：
No, it's not valid HTML5. You can easily see this by running the following fragment through a validator such as W3C's:
<!DOCTYPE html><title>�</title>
这将导致以下错误：
第1行，第27列：字符引用扩展为零。
Line 1, Column 27: Character reference expands to zero.
特定的代码点是规范中列出了不合法的字符引用（ W3C HTML5 ， WHATWG HTML Living Standard ）：
The specific code points that are not legal in character references are listed in the spec (W3C HTML5, WHATWG HTML Living Standard):
上述数字字符引用形式允许引用U + 0000，U + 000D以外的任何Unicode代码点，永久未定义的Unicode字符（非字符），代理（U + D800-U + DFFF）和空格字符以外的控制字符。
The numeric character reference forms described above are allowed to reference any Unicode code point other than U+0000, U+000D, permanently undefined Unicode characters (noncharacters), surrogates (U+D800–U+DFFF), and control characters other than space characters.
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