对于哪些html5属性是“空属性语法”，允许？ [英] For which html5 attributes is the "empty attribute syntax" allowed?
问题描述
http://www.w3.org/ TR / html-markup / syntax.html＃syntax-attr-empty 表示
空属性语法
某些属性可以通过仅提供属性名称来指定，没有值[...]完全等同于将空字符串指定为属性的值。
Empty attribute syntax
Certain attributes may be specified by providing just the attribute name, with no value [… which] is exactly equivalent to specifying the empty string as the value for the attribute.
IIRC，布尔属性经常使用它。但是，某些属性是指什么？ 允许此语法在哪些属性中使用哪种元素？或者：不允许在哪里？
IIRC, boolean attributes often use this. However, what does "certain attributes" refer to? In which attributes, on which elements, is this syntax allowed? Or: where is it not allowed?
我找不到完整的列表任何地方。
I could not find a complete list anywhere.
推荐答案
空属性语法只是具有名称和空字符串值的属性的简写，并且没有这本身就意味着什么特别的东西。因此，除了布尔属性之外，任何允许空值的属性，包括 class ，都可以使用空属性语法和任何不允许空值的属性来指定，例如如 id 和类型，不能使用空属性语法指定。
The empty attribute syntax is just a shorthand for an attribute with a name and an empty-string value, and doesn't mean anything special on its own. So, other than boolean attributes, any attribute that permits empty values, including class, can be specified with empty attribute syntax, and any attribute that doesn't permit empty values, such as id and type, cannot be specified with empty attribute syntax.
您可以使用 Validator.nu 比较以下代码段的验证结果来确认这一点。
You can confirm this by comparing the validation results of the following snippets using Validator.nu.
以下两个片段都应该验证：
Both of the following snippets should validate:
<!DOCTYPE html><title>Test</title>
<body class>
<!DOCTYPE html><title>Test</title>
<body class="">
以下两个代码段都应产生相同的验证错误：
And both of the following snippets should produce the same validation error:
<!DOCTYPE html><title>Test</title>
<body id>
<!DOCTYPE html><title>Test</title>
<body id="">
错误：属性
id <的值不正确元素body上的/ code>：ID不能是空字符串。
Error: Bad value for attribute
idon elementbody: An ID must not be the empty string.
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