问题描述
我正在使用HTML处理多个项目，有时我忘了放<！DOCTYPE html> 。
很多IDE允许用户将其忽略，并默认使用特定的HTML。样式，但将其保留下来确实会对浏览器兼容性和旧版HTML的使用造成潜在威胁。 例如：新功能& HTML5中的标记，例如<！DOCTYPE> 。
<！DOCTYPE> 声明不是HTML标记；
< article> ，<页脚> ，< header> ，&n; nav> ，<$ c如果未声明<！DOCTYPE> ，则可能不支持$ c>< section>
此外，浏览器可能会决定自动进入怪癖或严格模式。
I'm working on several projects with HTML, and sometimes I forget to put <!DOCTYPE html>. Will it make any big or noticeable changes?
The <!DOCTYPE> declaration must be the very first thing in your HTML document, before the tag.
The <!DOCTYPE> declaration is not an HTML tag; it is an instruction to the web browser about what version of HTML the page is written in.
A lot of IDEs allow users to leave this out and default to a certain HTML style, but leaving it out does pose a potential threat in browser compatibility and the use of older versions of HTML.
For example: new features & tags in HTML5 such as <article>,< footer >, <header>,<nav>, <section> may not be supported if the <!DOCTYPE> is not declared.
Additionally, the browser may decide to automatically go into Quirks or Strict Mode.
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