Detailed introduction to the use of DOCTYPE tags-HTML Tutorial-php.cn

Detailed introduction to the use of DOCTYPE tags

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Release： 2017-05-09 14:17:21

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The

declaration comes first in the document, before the tag. Tell the browser's parser what Document Type Specification should be used to parse this document.

The meaning of the statement
Only determines a correct document type, tags and cascading styles in Hypertext Markup Language or Extensible Hypertext Markup Language The table can take effect, even affecting the JavaScript script.

Compare the document type declaration

 <!DOCTYPE html><!--html5文档类型声明-->
 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 
   "http://www.w3.org/TR/html4/strict.dtd">
  <!--上是HTML 4.01 Strict-->

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Explanation

## declaration is not an HTML tag; it is an instruction that instructs the web browser as to which version of HTML the page should be written in.
In HTML 4.01, the declaration
references the DTD because HTML 4.01 is based on SGML. A DTD specifies the rules for a markup language so that browsers can render content correctly.
HTML5 is not based on SGML, so there is no need to reference a DTD.

Explanation

In order to promote the development of the Web standardization movement, some companies have joined forces to An organization called the Web Hypertext Application Technology Working Group (WHATWG) was established.
WHATWG focuses on Web forms and applications, while W3C (World Wide Web Consortium, World Wide Web Consortium) focuses on XHTML2.0. In 2006, the two parties decided to collaborate to create a new version of HTML.
On December 17, 2012, the World Wide Web Consortium (W3C) officially announced that the HTML5 specification, which has condensed the efforts of a large number of network workers, has been officially finalized. According to the W3C speech: "HTML5 is the cornerstone of the open Web network platform."
SGML (Standard General Markup Language)
is a way to define the structure and description of electronic documents International standard language for its content.
XML (Extensible Markup Language) is a subset of SGML, which became a W3C recommendation on February 10, 1998. XML is the most commonly used tool for data transfer between various applications.
html Hypertext Markup Language
An application under the Standard General Markup Language, HTML initially tried to become a subset of SGML, but HTML 4 did not strictly comply with SGML before standard. Later came HTML4, XHTML (HTML that conforms to the XML standard), both of which conform to the requirements of SGML.
html5

The article is excerpted from Encyclopedia and Zhihu

It can be seen that HTML5 is not based on SGML, but a more simplified and lightweight markup language.
So when using html5, when defining the document type at the beginning of the document, it can be directly simplified
```
     <!DOCTYPE html>
```
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Previously based on sgml, it was necessary to define such a document type within the document
HTML PUBLIC "-//W3C //DTD...
##DTD
means: document type definition DTD (Document Type Definition)Document type definition is a set of The syntax rules of tags. It is part of the Standard Universal Markup Language and Extensible Markup Language version 1.0 specifications. It is a verification mechanism for documents to see whether the document conforms to the specification and whether the elements and tags are used. Correct.
##I found that the grammar rules on DTD do not include html5.
##[Related recommendations 】

Free html online video tutorial

2. html development manual

3. php. cn original html5 video tutorial

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