HTML <meta http-equiv="X-UA-Compatible" content="IE=edge" />
It's a horrible hack to cater for different bugs or incomplete implementations in various versions of the Internet Explorer browser. For example, this:
if you need more deatail about read below content ......
Depending upon what Microsoft browsers you support you may not need to continue using the X-UA-Compatible tag. If you need to support IE9 or IE8, then I would recommend using the tag. If you only support the latest browsers (IE11 and/or Edge) then I would consider dropping this tag altogether. If you use Twitter Bootstrap and need to eliminate validation warnings, this tag must appear in its specified order. Additional info below:
The X-UA-Compatible meta tag allows web authors to choose what version of Internet Explorer the page should be rendered as. IE11 has made changes to these modes; see the IE11 note below. Microsoft Edge, the browser that replaced IE11, only honors the X-UA-Compatible meta tag in certain circumstances. See the Microsoft Edge note below.
According to Microsoft, when using the X-UA-Compatible tag, it should be as high as possible in your document head:
If you are using the X-UA-Compatible META tag you want to place it as close to the top of the page's HEAD as possible. Internet Explorer begins interpreting markup using the latest version. When Internet Explorer encounters the X-UA-Compatible META tag it starts over using the designated version's engine. This is a performance hit because the browser must stop and restart analyzing the content.
October 2015 Update
This answer was posted several years ago and now the question really should be should you even consider using the X-UA-Compatible tag on your site? with the changes Microsoft has made to its browsers (more on those below).
Depending upon what Microsoft browsers you support you may not need to continue using the X-UA-Compatible tag. If you need to support IE9 or IE8, then I would recommend using the tag. If you only support the latest browsers (IE11 and/or Edge) then I would consider dropping this tag altogether. If you use Twitter Bootstrap and need to eliminate validation warnings, this tag must appear in its specified order. Additional info below:
The X-UA-Compatible meta tag allows web authors to choose what version of Internet Explorer the page should be rendered as. IE11 has made changes to these modes; see the IE11 note below. Microsoft Edge, the browser that replaced IE11, only honors the X-UA-Compatible meta tag in certain circumstances. See the Microsoft Edge note below.
According to Microsoft, when using the X-UA-Compatible tag, it should be as high as possible in your document head:
If you are using the X-UA-Compatible META tag you want to place it as close to the top of the page's HEAD as possible. Internet Explorer begins interpreting markup using the latest version. When Internet Explorer encounters the X-UA-Compatible META tag it starts over using the designated version's engine. This is a performance hit because the browser must stop and restart analyzing the content.
Here are your options:
"IE=edge" "IE=11" "IE=EmulateIE11" "IE=10" "IE=EmulateIE10" "IE=9" "IE=EmulateIE9 "IE=8" "IE=EmulateIE8" "IE=7" "IE=EmulateIE7" "IE=5" To attempt to understand what each means, here are definitions provided by Microsoft: