HTML tutorial: WEB standards from scratch_DOCTYPE statement

On earlier web pages, we can often see the following web page structure code:

< ;meta name=”…” content=”…” />

…

…

Obviously, the web page code with this structure does not comply with Web standards, but the browser can still render this web page well, as long as there are no errors in the code. In fact, this is just like a page with a Table layout and a page with a Div structure. The browser can render it. The key is which page will render with higher quality.

There is a long distance between making a page and making a page.

In the development process of browsers, Microsoft has always become the dominant player in the browser market by bundling Internet Explorer into the Windows operating system. This has also resulted in a series of IEs that ignore the Web standards set by the W3C organization. Regarding the matter, Microsoft's IE has always only followed its own Web standards. Fortunately, Microsoft has decided to support Web standards in IE8, although this matter has not yet been finalized. In addition to Microsoft's IE, browsers such as Mozilla Firefox, Apple Safari, Opera, and Chrome have been fighting against IE for a long time in the name of supporting Web standards.

Differences in browsers result in different default parsing of HTML codes, so even the same code may appear in different styles under different browsers, so this requires a copy that all browsers follow Rules to coordinate differences between browsers, this rule requires a declaration to reference it, this declaration is DOCTYPE - document type (document type).

The DOCTYPE declaration is an essential part of a standard web page. Therefore, if you want to create a web page that complies with W3C standards, you first need to declare a document type for this page. There are three types of DTD (document type definition) declared by DOCTYPE, namely:

Transitional (transitional): a DTD with less strict requirements, allowing you to continue to use HTML4.01 tags in the page;

Strict ( Strict): This is the ideal DTD method when making pages, but this document type definition does not allow the use of any tags and attributes on the presentation layer;

Frameset (Frameset): This is specifically for pages that contain frames in their design. DTD.

Due to the impact that frame-type design may have on the inclusion of web pages in search engines, many web pages do not use frame design; and Strict DTD is just an ideal way for most people; Transitional DTD It is currently the most applicable and widely used document type definition. Now, if you open any web page that complies with Web standards, you can see this statement at the beginning of the page:

This is a DOCTYPE statement about an XHTML web document. Of course, this does not mean that the DOCTYPE statement can only be used for XHTML web documents. For web documents using HTML4.01, the DOCTYPE statement can also be used:

Transitional DTD:

Strict DTD:

The only thing to note is that the position of the DOCTYPE declaration must be at the very beginning of the page, at No code or tags can appear before the DOCTYPE declaration code, otherwise the tags or CSS styles on the page may become invalid.

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