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INFO: The "About:" Protocol in Internet Explorer

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This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
Summary
Internet Explorer 4.0 supports a number of special protocol schemes.One of these is the "about:" protocol, which is used to display descriptiveHTML pages for various predefined "about:" strings.

For example, "about:NavigationFailure" directs Internet Explorer to displaya brief page with more information about why a navigation might have failedand helpful hints for avoiding this error in the future.

Microsoft now supports an about: protocol that works as follows. If youenter a URL "about:example", MSHTML (the HTML parsing and rendering enginefor Internet Explorer 4) looks in the registry under "HKML\SOFTWARE\Microsoft\InternetExplorer\AboutURLs" for an string value named "example" and then loads theURL associated with it. If it cannot find the value "example," it generatesand displays a page "<HTML>example</HTML>."
More information
"about:" URLs have a simple form:
about:<string>
where <string> should be a simple combination of alphanumeric characters.

When resolving "about:<string>" URLs, Internet Explorer will look for astring value with a name that matches <string> under the registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AboutURLs
If found, Internet Explorer will load the content from the URL specified inthe value and display this in the browser window. It is acceptable to usedifferent protocols in referring to the content location; in fact, allpredefined "about:" protocols refer to "res:" URLs, which load HTML contentfrom DLL resources.

For example, "NavigationFailure" is listed as a value name under theaforementioned registry entry that has a string data value of"res://shdoclc.dll/navcancl.htm" on Internet Explorer 5.

If Internet Explorer does not find a match between <string> and a string value in this location, Internet Explorer will enclose <string> in <HTML> start and end tags and render it as HTML content.

NOTE: Other than the about:URLs included under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\InternetExplorer\AboutURLS, about:URLs serve no purpose. For security reasons, as of the release of Microsoft Internet Explorer 6.0 Service Pack 1, when you resolve "about:<string>" URLs, Internet Explorer causes navigation to fail.
References
Internet Client SDK: Internet Tools & Technologies; Predefined Protocols

Properties

Article ID: 183978 - Last Review: 06/22/2014 18:54:00 - Revision: 4.0

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