blocks|key|597548|text|根据latest+spec，您应该为<!DOCTYPE+html>使用不区分大小写的匹配项。因此，虽然浏览器需要支持您喜欢的任何情况，但从这一点可以合理地推断<!DOCTYPE+html>是典型的情况。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|597549|entityMap|0|LINK|mutability|MUTABLE|url|http://www.whatwg.org/specs/web-apps/current-work/multipage/syntax.html#the-doctype^0|I|F|27|F|2|B|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

According to the <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/syntax.html#the-doctype" rel="noreferrer">latest spec</a>, you should use something that is a case-insensitive match for <code>&lt;!DOCTYPE html&gt;</code>. So while browsers are required to support whatever case you prefer, it's reasonable to infer from this that <code>&lt;!DOCTYPE html&gt;</code> is the canonical case.

blocks|key|813078|text|大写或小写都是“正确的”。但是，如果你使用网页字体并关心IE7，我会推荐使用<!DOCTYPE+html>，因为IE7中有一个bug，如果使用<!doctype+html>+(例如this+answer)，网页字体有时会失败。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|813079|这就是为什么我总是把doctype大写。|813080|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/21166601/3515416^0|12|F|1Z|F|2I|B|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

Either upper or lower case is "correct". However if you use web fonts and care about IE7, I'd recommend using <code>&lt;!DOCTYPE html&gt;</code> because of a bug in IE7 where web fonts sometimes fail if using <code>&lt;!doctype html&gt;</code> (e.g. in <a href="https://stackoverflow.com/a/21166601/3515416">this answer</a>).

This is why I always upper-case the doctype.

blocks|key|597627|text|这个问题暗示着只有一个正确的答案，提供了两个多项选择，并要求我们选择一个。我建议对于HTML5，<!DOCTYPE+html>和<!doctype+html>都是有效的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|597628|因此，支持HTML5的浏览器将接受小写的html，并正确处理html。|597629|我听说，以前的浏览器和没有使用HTML5的浏览器，即使没有文档类型，也会尽可能地处理html。如果他们不能识别小写的doctype，他们也会这么做。因此，没有必要将其设为大写，因为这些浏览器无论如何都无法完全实现任何HTML5声明。|597630|entityMap^0|1C|F|1S|F|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|R|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|K|$]]

The question sort of implies there's only one correct answer, supplies a multiple choice of two, and asks us to pick one. I would suggest that for HTML5 both <code>&lt;!DOCTYPE html&gt;</code> and <code>&lt;!doctype html&gt;</code> are valid. 

So a HTML5-capable browser would accept the lowercase one and process the html properly. 

Browsers previous and oblivious to HTML5, I've heard, even without a doctype, will attempt to process the html as best they can. And if they don't recognize the lowercase doctype will do the same. So there's no point in making it uppercase since those browsers won't be able to fully implement any HTML5 declarations anyway.

blocks|key|597665|text|doctype声明不区分大小写，匹配的任何ASCII字符串|type|unstyled|depth|inlineStyleRanges|entityRanges|data|597666|Html5+standard|offset|length|597667|entityMap|0|LINK|mutability|MUTABLE|url|https://html.spec.whatwg.org/multipage/syntax.html#the-doctype^0|0|0|E|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

The doctype declaration is case insensitive, and any string of ASCII that matches 

<a href="https://html.spec.whatwg.org/multipage/syntax.html#the-doctype" rel="nofollow noreferrer">Html5 standard</a>

When writing the HTML5 doctype what is the correct method?

<pre><code>&lt;!DOCTYPE html&gt;
</code></pre>

or

<pre><code>&lt;!doctype html&gt;
</code></pre>

Uppercase or lowercase doctype?

HTML5

在编写HTML5文档类型时，正确的方法是什么？<!DOCTYPE html>或<!doctype html>

问doctype是大写还是小写？
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问doctype是大写还是小写？
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