about: URI scheme
From Seo Wiki - Search Engine Optimization and Programming Languages
about: is an internal URI scheme (also known as a "URL scheme" or, erroneously, "protocol") in various web browsers to display certain built-in functions. It is not an officially registered scheme, and has no standard syntax.
In early versions of Netscape, any address beginning
about: which wasn't recognised as a built-in command would simply result in the text after the colon being displayed. Similarly, in early versions of Internet Explorer,
about: followed by a string of HTML (e.g.
about:<em>hello world</em>) would render that string as though it was the source of the page - thus providing a similar (though more limited) facility to the data: URI scheme defined by RFC 2397. Still other versions of Netscape would return various phrases in response to an unknown
about: address, including "Whatchew talkin' 'bout, Willis?" (a catch phrase from the TV show Diff'rent Strokes) or "Homey don't play dat!" (from a recurring skit on the TV show In Living Color).
The most commonly implemented about: URIs are
about:blank, which displays a blank HTML document, and simply
about:, which may display information about the browser. Opera uses URIs beginning with opera: for similar purposes, and many about: URIs will be translated into an appropriate opera: URI if entered; an exception is
about:blank, which is not translated.
Note: In more recent versions of Internet Explorer, many of the following do not work or have been removed.
There are efforts to standardise the about URI scheme and define the processing requirements for some specific URIs. The about URIs that are known to be defined for specific purposes are listed below.
|about:blank ||Returns a blank HTML document with the media type text/html and character encoding UTF-8. This is widely used to load blank pages into browsing contexts, such as iframes within HTML, which may then be modified by scripts.|
|about:legacy-compat||A reserved, though unresolvable address defined within HTML5 intended for use in the DOCTYPE designed for compatibility with some legacy authoring tools, such as XSLT, which may not be capable of outputting the more common, shorter alternative that lacks both the PUBLIC and SYSTEM identifers. |
|about:srcdoc||A reserved, though unresolvable address defined within HTML5 intended to be the address navigated to within iframes whose content comes from the srcdoc attribute|
Common about: addresses
|Addresses||Mozilla / SeaMonkey||Mozilla Firefox||Opera||Internet Explorer||Konqueror||Safari||Google Chrome||MSN Explorer|
|about:||Shows version information and copyright information||Translated to "opera:about"||Translated to "about:konqueror"||Shows version information and copyright information||Shows a blank page|
|about:about||Lists all the about: addresses||Translated to "opera:about"||Translated to "about:konqueror"||Shows nothing but the text:"about"|
|about:blank||Shows a blank HTML document|
|about:plugins||Shows the filename, MIME type, description, suffix, and status of all installed plug-ins||Translated to "opera:plugins"||Shows the filename, MIME type, description, suffix, and status of all installed plug-ins||Shows the filename, MIME type, description, suffix, and status of all installed plug-ins|
|about:cache||Shows information about the Cache Service.||Translated to "opera:cache"||Translated to "about:konqueror"|| Lists the URIs of pages stored within the cache, with each linking to |
|about:mozilla||Shows a page from the fictional Book of Mozilla. In some versions of Netscape, also replaced the meteors in the standard Netscape throbber with a large fire-breathing lizard.||The Windows version of IE showed a blank HTML document with blue background color. Possibly a joke reference to the "Blue Screen of Death". Removed in Windows XP SP2 but it can still be shown by typing "res://mshtml.dll/about.moz" instead.||Translated to "about:konqueror"|
Mozilla-specific about: addresses
|Addresses||Mozilla Application Suite / SeaMonkey||Mozilla Firefox|
|about:bloat||Displays BloatView output (disabled in release builds).|
|about:blocked||Shows the malware protection page used when the browser identifies a page as not safe for viewing. (Firefox 3-specific).|
|about:buildconfig||Shows the arguments and options used to compile the build in use|
|about:cache||Shows information about the Cache Service. Number of entries, location of cache, size of cache, etc. for both memory and disk cache.|
|about:cache?device=memory||Shows individual entries in memory|
|about:cache?device=disk||Shows individual entries on disk|
|about:cache?device=offline||Shows individual entries for offline viewing. New to products based on Gecko 1.9 or later.|
|about:cache-entry||Shows information about a cache entry. Used in about:cache links. Requires parameters.|
|about:certerror||Shows the error page used when an SSL/TLS certificate is untrusted or otherwise invalid.|
|about:config||Shows an interface for viewing and setting a wide variety of configuration variables, many of which are not otherwise accessible through the GUI (options panels)|
|about:crashes||Shows details of crashes submitted by Mozilla's crash reporter (since Firefox 3).|
|about:credits||Shows a list of all those who contributed to Mozilla|
|about:licence||In the British English localised version, shows the content of about:license but with all occurrences of license used as a noun replaced with licence (see American and British English spelling differences)|
|about:license||Shows the Mozilla Public License (and the Netscape Public License) for the piece of software. (Only in products based on Gecko 1.8 or later)|
|about:logo||Shows the logo used on the about: screen|
|about:memory||Shows memory usage (since Firefox 3.6)|
|about:mozilla||Easter egg: Shows a verse from The Book of Mozilla|
|about:neterror||Shows the error page used when the browser could not access the requested path.|
|about:plugins||Shows installed plug-ins.|
|about:robots||Easter egg, beginning with March 8, 2008 trunk builds.|
|about:rights||Shows licensing information.|
|about:jetpack||Shows an interface for viewing and setting the JetPack plug-in |
|about:sessionrestore||Shows an interface for viewing about last session|
|about:privatebrowsing||Can be used to switch to private browsing mode, shows a message indicating that Firefox will not remember any history for the current session. Note: It does not show URI on the address bar.|
Flock-specific about: addresses
Beginning in Flock 0.9, Flock introduced a feature called My World, a place where the user's favorites, RSS feeds and favorite media can be found.
|about:myworld||Shows the My World page.|
|about:tutorial||Shows the Flock tutorial page.|
|about:mozilla||Shows a different version of The Book of Mozilla against a blue screen.|
Opera-specific about: addresses
|opera:blank||Maps to about:blank|
|opera:about||Provides info about the browser and the configured paths.|
|about:opera||Maps to opera:about|
|opera:cache||Shows the content of the cache.|
|opera:config||(Opera 9.0 and newer) Shows a page that allows changing of numerous browser preferences, many of which cannot be accessed through the normal Preferences window|
|opera:drives||(Operating system specific) Shows the local drives of the host system.|
|opera:history||Shows the content of the browser history.|
|opera:historysearch||(Opera 9.5 and newer) Shows the start page of internal search engine for the browser history.|
|opera:plugins||Shows installed plug-ins.|
|opera:button||Defines a custom button as a set of Opera actions. (Note: This does not work directly, you need to specify all button parametres as on CustomButtons.)|
|opera:help||Shortcut to the help directory. This can be either local or external.|
|opera:debug||(Opera 9.5 and newer) Shows a page that allows changing of settings for remote debug of Opera via Opera Dragonfly|
|opera:memdebug||(Opera 9.5 and newer) Shows debug information about memory usage.|
Internet Explorer-specific about: addresses
Note: Internet Explorer about: addresses are configurable in Windows. It is therefore possible that some of the listed addresses don't work. For example "about:mozilla" was removed in SP2 (although the page can still be found at "res://mshtml.dll/about.moz"). These about: addresses are sometimes used for spyware and adware, most notably in CoolWebSearch, which made about:blank display advertisements.
|Address||Internet Explorer 6(SP2)||Internet Explorer 7||Internet Explorer 8|
|about:Home||Displays the user's home page.|
|about:Blank||Displays the blank page.|
|about:DesktopItemNavigationFailure||Displays "navigation cancelled" page.|
|about:NavigationCanceled||Displays "navigation cancelled" page.|
|about:NavigationFailure||Displays "navigation cancelled" page.|
|about:NoAdd-ons||Displays information page when add-ons are disabled.|
|about:NoAdd-onsInfo||Displays information page about the effects when you use add-ons.|
|about:OfflineInformation||Informs the user that the current page can not be viewed off line.|
|about:PostNotCached||Informs the user that to refresh the current page, information entered in a form will have to be re-posted.|
|about:SecurityRisk||Informs the user not to browse with the current security settings because they may be harmful to the computer.|
|about:Tabs||Informs the user about tabbed browsing. It is also loaded when a new tab is created if the "Open home page for new tabs instead of a blank page" setting is enabled|
|about:inprivate||Informs the user about InPrivate Browsing. It is loaded when InPrivate Browsing is initiated.|
Google Chrome-specific about: addresses
|about:cache||Shows the content of the cache.|
|about:crash||Displays "Aw, snap!" crash notification page.|
|about:credits||Displays the list of free and open source software used in the browser, and their associated licences.|
|about:dns||Displays the DNS records|
|about:inducebrowsercrashforrealz||Crashes the Google Chrome browser. This is designed for developers to test what happens when the Google Chrome browser crashes.|
|about:internets||Displays a page entitled "Don't Clog the Tubes!" which renders a page with an animation of the Microsoft Windows "3D Pipes" screensaver. Does not work on Windows Vista due to the pipes screen saver no longer being supported or releases after the 220.127.116.11 release.|
|about:memory||Displays the process manager|
|about:network||Provides an interface for monitoring the network usage and performance statistics|
|about:plugins||Shows installed plug-ins.|
|about:stats||Displays statistics about processes. At the top of the page, it states "Shhh! This page is secret!"|
|about:shorthang||Hangs the tab's process, making it become unresponsive. This is designed for testing the hanging protection.|
|about:version||Displays version information, same as about:|
Note: Any "about:" URI is accepted, but only a page with a blank source is returned, as with the "about:blank" of other browsers. Similar to Safari.
Note: Any "about:" URI except "about:blank" and "about:plugins" redirects to "about:konqueror".
|about:konqueror||Shows a friendly 'start' and navigation page|
Additionally, about:epiphany yields a quote attributed to Antoine de Saint-Exupéry:
Il semble que la perfection soit atteinte non quand il n'y a plus rien à ajouter, mais quand il n'y a plus rien à retrancher.—Antoine de Saint-Exupéry
Translated as: It seems that perfection is attained not when there remains nothing to add, but when there remains nothing to remove. This can be seen as a rejoinder to critics who claim that the browser's (and the GNOME desktop's) focus on usability has led to a lack of features.
- Older versions of the Netscape browser have an about:people URL that was similar to about:credits above, but it would redirect to Netscape's active employee listing. In addition, about:username, where username is the username of a Netscape employee, would redirect to the Netscape homepage of the employee specified. For example, about:jwz would redirect to http://people.netscape.com/jwz/ (not an active link)  .
- Not all employee pages were accessible through this scheme. Only developers who knew which file in the source tree and the encoding scheme used to obfuscate the directory of employee about entries could add their names.
- Many other about: easter eggs existed, including the famous about:mozilla, and other less known ones that showed pictures of the Netscape mascot Mozilla in various foreign garb, such as about:deutsche showing Mozilla in Lederhosen.
- Some versions of Netscape would display the browser history for the about:global address
about: URI is accepted, but only a page with a blank source is returned, as with the
about:blank of other browsers.
In Microsoft Outlook, an additional outlook:today URI was added, which showed the Outlook Today Screen (it shows messages, tasks and appointments and is also accessible from IE). Also, although about:blank is supported, anything else (including about:about) typed after about: would show that text as a web page in the browser.
- IETF draft specification for the about: URI scheme
- About protocol links in Mozilla and Mozilla Firefox.
- about redirectors' source code in firefox
Notes and References
- ^ The 'about' URI scheme (IETF draft)
- ^ The term "about:blank" is also the generic name for a group of variants of the CoolWebSearch malware program group.