关于http-equiv = "X-UA-Compatible"？

<meta http-equiv = "X-UA-Compatible" content = "IE=7" >

#以上代码告诉IE浏览器，无论是否用DTD声明文档标准，IE8/9都会以IE7引擎来渲染页面。  

<meta http-equiv = "X-UA-Compatible" content = "IE=8" >

#以上代码告诉IE浏览器，IE8/9都会以IE8引擎来渲染页面。  

<meta http-equiv = "X-UA-Compatible" content = "IE=edge" >   

#以上代码告诉IE浏览器，IE8/9及以后的版本都会以最高版本IE来渲染页面。  

<meta http-equiv = "X-UA-Compatible" content = "IE=7,IE=9" >   

<meta http-equiv = "X-UA-Compatible" content = "IE=7,9" >   

<meta http-equiv = "X-UA-Compatible" content = "IE=Edge,chrome=1" >

#以上代码IE=edge告诉IE使用最新的引擎渲染网页，chrome = 1则可以激活Chrome Frame