main 元素中的内容对于文档来说应当是唯一的。它不应包含在文档中重复出现的内容，比如侧栏、导航栏、版权信息、站点标志或搜索表单。
注释：在一个文档中，不能出现一个以上的 main 元素。main 元素不能是以下元素的后代：article、aside、footer、header 或 nav。
using mainmy page [url=#]home[/url] my article content more information copyright 2013
另一个例子:
skateboards the skateboard is the way cool kids get around longboards longboards are a type of skateboard with a longer wheelbase and larger, softer wheels. ... ... electric skateboards these no longer require the propelling of the skateboard by means of the feet; rather an electric motor propels the board, fed by an electric battery. ... ...
html 5中又新增加main标签
the main element