Detailed explanation of the difference between IE8 compatibility view (IE7 mode) and standalone IE7

Detailed explanation of the difference between IE8 compatibility view (IE7 mode) and standalone IE7

one. Overview of IE8 Compatibility View <br />In order to solve the problem that the new version of the browser is incompatible with old websites, IE8 browser has added a feature called "Compatibility View", which allows web pages to be displayed according to IE7 code specifications. This can solve most (but not all) web page problems caused by inconsistent code standards.
two. Difference between "browser mode" and "document mode"
 Compatibility view involves two important functions: "browser mode" and "document mode". In IE8, press F12 to open "Developer Tools". In the menu bar, you can see the switching menu of "browser mode" and "document mode", where you can choose to switch to different web page modes such as IE7/8.
So what is the difference between "browser mode" and "document mode"?
"Browser Mode" is used to switch IE's default document mode for the web page, parse conditional comments for different versions of browsers, and the value of the User-Agent string sent to the website server. The website can determine the browser version and installed functions based on the different user agent strings returned by the browser, so that different page content can be returned to different browsers.
By default, the browser mode of IE8 is IE8. Users can manually switch to a different browser mode by clicking the Compatibility View button next to the address bar. In IE8, the IE8 compatibility view will display the web page in IE7 document mode and send the IE7 user agent string to the server.
"Document mode" is used to specify which version of IE's page layout engine (Trident) should use to parse and render web page code. Switching document modes causes the web page to be refreshed, but does not change the version number in the user agent string, nor does it re-download the web page from the server. When you switch the browser mode, the browser will automatically switch to the corresponding document mode.
Generally speaking, both should be set to the same version, but what if they are different? Or is there a priority difference between the two?
Please see the following MSDN post: 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
Highlights:
•We've evangelized use of the X-UA-Compatible tag to websites unable to update to support IE8's Standards mode. The tag allows a web author to declare the exact standards mode behavior for which their website works best – IE8 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”.
•We've 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 haven't 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 to – IE8 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 can't affect the UA string as it's already too late to change that – the client's 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) won't make your website compatible – you'll also need to update your User Agent string detection logic as well.
In summary, there are two ways to make IE8 compatible with IE7 mode. One is on the server side, by having the programmer control and modify the document mode of the web page, that is, through Meta (X-UA-Compatible IE=EmulateIE7), to force the page to become compatible with IE7.
as follows:

Copy code
The code is as follows:

<head runat="server">
<meta http-equiv="X-UA-Compatible" content="IE=7" />
<title>cest</title>
</head>

If you don't write this sentence, IE8 will be used by default.
The other is on the client side. When the website has not had time to modify the Meta, if the user has installed IE8 and finds that it cannot display normally, the last resort is to click the Compatibility View button, which is ultimately reflected in the User Agent. That is to say, after clicking the Compatibility View button, the submitted Http request header will be rewritten as MSIE7.0, causing the client to disguise itself as IE7 to send the request.
as follows:
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; Trident/5.0; SLCC1; .NET CLR 2.0.50727; .NET CLR 3.0.30729; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E)
According to MSDN, modifying Meta (X-UA-Compatible IE=EmulateIE7) has higher priority than clicking Compatibility View. It can override the selection of Compatibility View. In other words, once the website is revised and released, as long as Meta is set, the Compatibility View set on the original user's browser can be invalidated, thereby automatically adapting to the new version of IE8 browser.
three. IE8 compatibility view (IE7 mode) is not exactly the same as standalone IE7
 See Technet.Microsoft's post:
What Is Compatibility View?
http://technet.microsoft.com/zh-cn/ff966533
Compatibility View is a feature of Windows Internet Explorer 8 that enables the browser to render a webpage nearly identically to the way that Windows Internet Explorer 7 would render it.
In Internet Explorer 8, Compatibility View changes how the browser interprets code that is written in CSS, HTML, and the Document Object Model (DOM) to try to match Internet Explorer 7. A site that a user views in Internet Explorer 8 Compatibility View is almost identical to a site that the user views in Internet Explorer 7. However, Compatibility View does not change how the browser interprets all code. For example, the changes in Internet Explorer 8 for how the browser handles ActiveX, the parser, AJAX, JavaScript, networking, and security might still cause compatibility issues. Compatibility View does not change these behaviors.
In an enterprise environment, some areas have lower risk for compatibility issues. For example, Intranet Zone websites use Compatibility View by default. Client web applications that render by using the Web Browser Control, or the WebOC (Internet Explorer rendering engine), also have a low risk for compatibility issues because Internet Explorer 8 defaults to a compatibility mode for the WebOC. However, the default configuration settings for Compatibility View might not ensure complete compatibility. To determine if a website or web application is compatible with Internet Explorer 8, you should test the website or web application.
For more information about the differences between Internet Explorer 8 Compatibility View and Internet Explorer 7, see the Site Compatibility and Internet Explorer 8 blog. For a list of what to check when you upgrade to Internet Explorer 8, see the Internet Explorer 8 Readiness Toolkit.
For more information about Compatibility View, see the Internet Explorer Team Blog.
See the MSDN post:
1. Differences between IE8 Compatibility View and IE7
http://blogs.msdn.com/b/ie/archive/2009/03/12/site-compatibility-and-ie8.aspx
excerpt:
We strive to make Compatibility View behave as much like IE7 as possible, but we do make exceptions. Many of these exceptions enable improved security and accessibility features immediately, even for sites that have not yet migrated to IE8 Standards Mode.
2. What EXACTLY does Compatibility View do in IE8?
http://webmasters.stackexchange.com/questions/2219/what-exactly-does-compatibility-view-do-in-ie8
Highlights:
Compatibility View renders the page as if it was Internet Explorer 7 (including Javascript). There are a few differences between IE8 with CV and pure IE7 but essentially it is the same. If you really want the detail of what is going on then read Just The Facts: Recap of Compatibility View from the IE MSDN blog.
You can also force IE8 to use CV with this meta tag:
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" />
If you are having problems, I'd suggest first checking you have a legitimate doctype in your HTML (the simplest one is <!DOCTYPE html> which forces standards mode). That will solve 90% of your problems, especially with IE6.
The conclusion is: IE8 compatibility mode is different from independent IE7, and there are still some differences. It does not simply include a complete IE7 in IE8.
Four. Details of the specific differences
 1. Cross Document Communication
Hacks enabling cross-domain, cross-document communication have been disabled for security reasons.
Solution: Use Cross Document Messaging (XDM) to work around this change.
2. Extending the Event Object
IE exposes new properties for certain AJAX features such as Cross Document Messaging (XDM), even in Compatibility View. Adding custom properties to the Event object can conflict with these new properties, such as "source".
event.source = myObject; // Read-only in IE8
Solution: Change the names of conflicting custom properties to avoid collision.
event.mySource = myObject;
3. Attribute Ordering
The ordering of attributes has changed, affecting the attributes collection as well as the values ​​of innerHTML and outerHTML. Pages depending on a specific attribute ordering may break.
attr = elm.attributes[1]; // May differ in IE8
Solution: Reference attributes by name as opposed to their position within the attributes collection.
attr = elm.attributes["id"];
4. Setting Unsupported CSS Values
Assigning CSS values ​​that were unsupported in IE7 but are supported in IE8 Standards Mode will not generate exceptions in IE8 Compatibility View. Some sites use these exceptions to determine if a particular value for a CSS property is supported or not.

Copy code
The code is as follows:

Try
{
elm.style.display = "table-cell";
} catch(e)
{
// This executes in IE7,
// but not IE8, regardless of mode
}

Solution: Short of version detection, this is a difficult issue to work around. If this behavior is essential to a page, updating the page to run in IE8 Standards Mode may be the best approach.

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