HTML5/CSS3 related knowledge explanation

When you encounter some common knowledge points in learning html and css, this article will explain them in detail.

What is HTML5? What are the new features? What new tags are there? How to make lower versions of IE support HTML5 new tags?

HTML5 is the fifth major revision of HTML. It has abandoned many redundant tags and also added many new tags, making HTML more semantic and richer in interactive functions.
In HTML5, it has many new features:
1. More semantic tags, giving web pages better meaning and structure;
2. Support local storage. The web APP has a shorter startup time, faster Internet speed
3, and device compatibility. External applications can be directly connected to the data inside the browser. For example, video and audio can directly interact with microphones and cameras
4, and the connection is faster. Implemented Server-Sent Event and WebSockets, enabling page-based real-time chat, faster web game experience, and more optimized online communication.
5, audio and video tag references, can embed multimedia content on the page
6. Based on svg, the three-dimensional, graphic and special effects characteristics of canvas

The following are some new tags and changes
1. About DOCTYPE

//Previous HTML "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">//HTML5< ;!DOCTYPE htm>

2. About meta

//Previous HTML//HTML5

3. New tag
canvas tag defines graphics, such as charts and other images. This tag is based on the JavaScript drawing API
audio defines audio content
video defines video (video or movie)
source defines multimedia resources

In the past, we used the

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