What is doctype and what does it do to the Web?

Web page

DOCTYPE is a shorthand for document type, which is used in web design to illustrate the version of XHTML or HTML that you use.

To create a standard Web page, the DOCTYPE declaration is an essential part of the key; unless your XHTML determines a correct DOCTYPE, your logo and CSS will not work.

　　DOCTYPE Statement

The first thing to do when you start making a site that meets the standard is to declare a DOCTYPE that meets your needs.

See a lot of Web sites developed using XHTML standards, the first line is:

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 transitional//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">

Open some standards-compliant sites, such as the famous web design software developerMacromedia, you will find the same code.

Some other standards-compliant sites have the following code:

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 frameset//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd" >

So what does the code mean? Are you sure you want to place it?

　　 What is DOCTYPE

The above code we call the DOCTYPE declaration. DOCTYPE is a shorthand for document type, which is used to indicate what version of XHTML or HTML you are using.

The DTD (for example, the XHTML1-TRANSITIONAL.DTD in the example above) is called the document type definition, which contains the rules of the document, and the browser interprets the identity of your page based on the DTD you define and displays it.

To create a standard Web page, the DOCTYPE declaration is an essential part of the key; unless your XHTML determines a correct DOCTYPE, your logo and CSS will not work.

XHTML 1.0 offers three types of DTD declarations to choose from:

* Transition (Transitional): A very loose DTD that allows you to continue using HTML4.01 's identity (but to conform to XHTML), the complete code is as follows:

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 transitional//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">

* Strict (Strict): Requires a strict DTD, you can not use any of the presentation layer of the identity and attributes, such as &LT;BR&GT, the complete code is as follows:

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 strict//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" >

* Framework (Frameset): A DTD specifically designed for frames page design, if your page contains frames, you need to use this DTD, complete code as follows:

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 frameset//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd" >

　　 What kind of doctype do we choose ?

Ideally, of course, a strict DTD, but for most of us who have just come in contact with Web standards, the transition DTD (XHTML 1.0 Transitional) is the ideal choice now. Because the DTD also allows us to use the identity, elements, and attributes of the presentation layer, it is also easier to pass the code checksum of the consortium.

Note: The above "performance layer identification, attributes" refers to those who are purely used to control the performance of the tag, such as the table used for typesetting, background color identification. The identity in XHTML is used to represent structs, not to implement representations, and the purpose of our transition is to ultimately achieve separation of data and performance.

For example, a mannequin changes clothes. Models are like data, clothes are representations, models and clothes are separate, so you can change clothes at will. The original HTML4, the data and performance is mixed together, it is very difficult to change the form of a one-time. Oh, a little abstract, this concept requires us to gradually understand in the application process.

　　 Supplements

The DOCTYPE declaration must be placed at the top of every XHTML document, above all code and logo.