【http-equiv】
Note that supplying an HTTP equivalent in a meta element is only effective if the server doesn’t send the corresponding real header; you can’t override an HTTP header with a meta element. So using this attribute is only of value when the server doesn’t send that particular header, or when there is no server involved—for instance, when you’re viewing a document from the local file system.
1、Examples.
2、The value of http-equiv varies depending on the way you use it. It may contain any of the following values:
参考：