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IE7 mode IE8兼容視圖與獨(dú)立IE7的區(qū)別詳解

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【IE7 mode IE8兼容視圖與獨(dú)立IE7的區(qū)別詳解】一． IE8兼容視圖概述
為了解決新版瀏覽器不兼容舊網(wǎng)站的問題，IE8瀏覽器增加了一種叫做兼容性視圖的功能，可以讓網(wǎng)頁以IE7的代碼規(guī)范來顯示，這樣，就能夠很好的解決大部分（但不是全部）由于代碼標(biāo)準(zhǔn)不一致引起的網(wǎng)頁問題 。
二．瀏覽器模式和文檔模式之間的區(qū)別
兼容性視圖涉及兩個(gè)重要的功能便是瀏覽器模式browser mode和文檔模式document mode，在IE8中按F12鍵，打開開發(fā)人員工具，在菜單欄中可以看到瀏覽器模式和文檔模式的切換菜單，其中可以選擇切換到IE7/8等不同的網(wǎng)頁模式 。
那瀏覽器模式和文檔模式之間有什么區(qū)別呢？
瀏覽器模式用于切換IE針對該網(wǎng)頁的默認(rèn)文檔模式、對不同版本瀏覽器的條件備注解析、發(fā)送給網(wǎng)站服務(wù)器的用戶代理（User-Agent）字符串的值 。網(wǎng)站可以根據(jù)瀏覽器返回的不同用戶代理字符串判斷瀏覽器的版本和安裝的功能，這樣就可以向不同的瀏覽器返回不同的頁面內(nèi)容 。
默認(rèn)情況下，IE8的瀏覽器模式為IE8 。用戶可以通過單擊地址欄旁邊的兼容性視圖按鈕來手動(dòng)切換到不同的瀏覽器模式 。在IE8中，IE8兼容性視圖會以IE7文檔模式來顯示網(wǎng)頁，同時(shí)會向服務(wù)器發(fā)送IE7的用戶代理字符串 。
文檔模式用于指定IE的頁面排版引擎（Trident）以哪個(gè)版本的方式來解析并渲染網(wǎng)頁代碼 。切換文檔模式會導(dǎo)致網(wǎng)頁被刷新，但不會更改用戶代理字符串中的版本號，也不會從服務(wù)器重新下載網(wǎng)頁 。切換瀏覽器模式的同時(shí)，瀏覽器也會自動(dòng)切換到相應(yīng)的文檔模式 。
一般來說，兩者都要設(shè)置為同樣的版本，但是，如果不同又如何呢？或者說兩者是否有優(yōu)先級區(qū)別呢？
請看下面的msdn帖子：Just The Facts: Recap of Compatibility View
http://blogs.msdn.com/b/ie/archive/2009/02/16/just-the-facts-recap-of-compatibility-view.aspx
精華摘抄：
Weve evangelized use of the X-UA-Compatible tag to websites unable to update to support IE8s Standards mode. The tag allows a web author to declare the exact standards mode behavior for which their website works bestIE8 Standards (again, the default when no header is present) or IE7 Standards. For example, using the value IE=EmulateIE7 causes IE8 to display a website as IE7 would have.
Weve provided end-user and corporate / IT mitigations to the website compatibility problem under the umbrella term Compatibility View. Compatibility View allows IE8 users to have a great experience even when visiting websites that havent yet performed either of the above two steps. It also helps IT organizations preserve compatibility with the large number of line-of-business websites that are Internet Explorer 7 capable today.
Compatibility View and the X-UA-Compatible tag are not equivalent. Compatibility View is something you do on the client. It affects three things: the User Agent string, the Version Vector (used in evaluation of conditional comments), and what mode DOCTYPEs that trigger Standards map toIE8 Standards or IE7 Standards. The X-UA-Compatible META tag / header is something you use in page content / server-side and, when present, completely overrides Compatibility View settings on the client. It affects two things: the Version Vector and what mode DOCTYPEs that trigger Standards map to. It cant affect the UA string as its already too late to change thatthe clients already made the GET request to the server (and it contains a UA string). What this means to developers is that if your site pivots on the User Agent string, adding just the X-UA-Compatible tag (to cause IE8 to display your site in IE7 Standards mode) wont make your website compatibleyoull also need to update your User Agent string detection logic as well.
總結(jié)，有兩種方式可以使IE8兼容IE7模式，一是在服務(wù)器端，通過程序員控制修改網(wǎng)頁的文檔模式document mode，也就是通過Meta（X-UA-Compatible IE=EmulateIE7）, 強(qiáng)制使頁面變?yōu)榧嫒軮E7的頁面 。

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