为什么 <img>标签未在 HTML 中关闭? [英] Why is the <img> tag not closed in HTML?
问题描述
出于好奇，为什么 HTML 中的 img> 标签没有关闭?
For curiosities sake, why is the <img> tag not closed in HTML?
<img src="smiley.gif" alt="Smiley face" height="42" width="42">
我还注意到 XHTML...
<img src="smiley.gif" alt="Smiley face" height="42" width="42"/>
W3Schools: 图片标签
推荐答案
从历史上看，HTML 一直基于 SGML，它允许在某些条件下省略标签.
Historically, HTML has been based on SGML which allows tags to be omitted under certain conditions.
由于 元素不能有任何子节点，它被定义为 EMPTY 并且禁止使用结束标记(因为它没有任何作用).
Since the <img> element cannot have any child nodes, it is defined as EMPTY and the end tag is forbidden (as it would serve no purpose).
XHTML 是用 XML 表示的 HTML，而 XML 不支持可选或禁止标签(尽管它允许自闭合标签代替开始+结束标签对)，因此必须在那里显式闭合.
XHTML is HTML expressed in XML, and XML does not support optional or forbidden tags (although it allows a self-closing tag to substitute for a start+end tag pair), so it has to be explicitly closed there.
HTML 5 向后兼容基于 SGML 的 HTML 版本.
HTML 5 is backwards compatible with versions of HTML that were SGML based.
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