什么<！doctype html>做？ [英] What does <!doctype html> do?
问题描述
这个标记是干什么的？
<！doctype html>
我能看到的是，在这个标签的顶部，我的html以另一种方式运行而不是没有。
我怎么知道我是否需要这个标签？
8.1.1 DOCTYPE
DOCTYPE是必需的序言。
由于遗留原因，DOCTYPE是必需的。省略时，浏览器倾向于使用与某些规范不兼容的不同渲染模式。在文档中包含DOCTYPE可确保浏览器尽力尝试遵守相关规范。 b $ b
编辑添加：
这个安全带是做什么的？
我能看到的是的，这个安全带上，我的汽车行为方式与没有。我怎么知道我是否需要这个安全带？
您不知道在出现问题之前您是否需要它，没有它。
What does this tag do?
<!doctype html>What I can see is that with this tag on top my html behaves in another way than without. How do I know if I need this tag?
解决方案It's an integral part of HTML as defined in the specification:
8.1.1 The DOCTYPE
A DOCTYPE is a required preamble.
DOCTYPEs are required for legacy reasons. When omitted, browsers tend to use a different rendering mode that is incompatible with some specifications. Including the DOCTYPE in a document ensures that the browser makes a best-effort attempt at following the relevant specifications.
Edit to add:
What does this seatbelt do?
What I can see is that, with this seatbelt on, my car behaves the same way as without. How do I know if I need this seatbelt?
You wont know if you'll need it until something goes wrong and you don't have it.
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