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What is HTML?
HTML is a markup language for describing web documents (web pages).
Example
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<h1>My First Heading</h1>
<p>My first paragraph.</p>
</body>
</html>
Example Explained
HTML Tags
HTML tags ar keywords (tag names) surrounded by angle brackets:
<tagname>content goes here...</tagname>
Web Browsers
The purpose of a web browser (Chrome, IE, Firefox, Safari) is to read HTML documents and display them.
The browser does not display the HTML tags, but uses them to determine how to display the document:
HTML Page Structure
Below is visualization of an HTML page structure:
<html>
<head>
<title>Page title</title>
</head>
<body>
<h1>This is a heading</h1>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
</body>
</html>
The <!DOCTYPE> Declaration
The <!DOCTYPE> declaration represents the document type, and helps the browser to display a web page correctly.
It must only appear once, at the top of the page (before any HTML tags).
There are different document types. To display a web page correctly, the browser must know both type and version.
The doctype declaration is not case sensitive. All cases are acceptable:
<!DOCTYPE html>
<!doctype HTML>
Common <!DOCTYPE> Declarations
HTML5 <!DOCTYPE HTML>
HTML4.01 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd"
XHTML1.0 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
HTML Versions
Version Year
HTML 1991
HTML2.0 1995
HTML3.2 1997
HTML4.01 1999
XHTML 2000
HTML5 2014
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原文地址：http://www.cnblogs.com/lostkite/p/5724665.html
