this is the main heading 

this text might be an introduction to the rest of the page ,and if the page is a long one

this is a sub-heading  

Many long acticles have sub_heading

Another Sub-Heading

Here you can see another sub-Heading

 

 

网页的组成

文本

图片 jpg， png

音频 mp3

视频 mp4

其中，HTML源码编辑器本身还有文件类型，文件类型的语言种类等元素，故可以省去<head></head>之间的代码