DOCTYPE document type declaration (a must-read for web page enthusiasts)_HTML/Xhtml_Web page production

Document Type Declaration
At the top of each of your pages, you need a document type declaration. Yes, it must.

If you don’t specify a document type, your HTML is not valid HTML, and most browsers will process the page in “quirks mode”, which means the browser thinks you don’t know it either. Exactly what to do, and handle your code in the browser's own way. You can be an HTML master, invincible in the world, or your HTML can be flawless, and your CSS can be perfect, but if there is no documentation declaration, or wrong documentation declaration, your web page is like a short-sighted, one-eyed The gibbon babies are stacked up with great difficulty.

The document declaration of XHTML 1.0 Strict is as follows:


The following is the document statement of XHTML 1.1. As the latest version of XHTML, it looks more perfect, but there are still some problems. Later we will explain a little bit

Note that the DOCTYPE tag must be capitalized and preceded by an English half-width exclamation mark!. It's the only tab that breaks the rules and it doesn't need to be closed.

Language Declaration
You must specify a primary language for the document even if the xml:lang attribute is set in the HTTP header or within the html start tag. Although this is not required to handle a valid XHTML document, it is a usability consideration. Values ​​are abbreviated, such as en (English, English), fr (French, French), de (German, German).

Declares a document with mainly English content. An example is as follows:


After declaring the main language, if you need to use other languages, you can also use the xml:lang attribute inline (such as HTML Hund< /span>).

Content-Type
The media type and font set of the HTML document may need to be specified, which can be done using HTTP headers, for example:
Content-Type: text/html; charset=UTF-8

The first part of the HTTP header (such as text/html) is the file MIME type, which lets the browser know the media type of the file so it can know how to process it. All files have MIME types. JPEG images are image/jpeg, CSS files are text/csss and HTML generally use text/html.

The second part of the HTTP header (like the UTF-8 part) is the character set.

Perhaps the easiest way to set HTTP headers is to use the "HTTP-equivalent" header tag in HTML, like this:

The following is a commonly used document declaration. In fact, Dreamweaver uses this declaration by default.

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The code is as follows:

The following is the supplementary content of Script House.
Declaring or not declaring css will result in different control of the page. It won't comply with w3c standards or anything like that. So I recommend everyone to add it. This will make your website compatible with multiple browsers.
The impact of JavaScript will be greater, causing the JS code written before to not run properly. Especially things like couplet ads. In fact, in general, just pay attention to the following issue.
Generally use document.body.scrollTop when not declaring;
Use document.documentElement.scrollTop when declaring a document type;
Here are some reference documents
Essential for writing cross-browser javascript code [js multi-browser compatible writing method]
javascript firefox compatible ie dom method script
This is so convenient There are more, you can search more.