Acid2 Explained

Type:Web standards test
Language:English language
Owner:The Web Standards Project
Author:Ian Hickson
Launch Date:April 13, 2005
Current Status:Online

Acid2 is a test page published and promoted by the Web Standards Project to expose web page rendering flaws in web browsers and other applications that render HTML. Named after the acid test for gold, it was developed in the spirit of Acid1, a relatively narrow test of compliance with the Cascading Style Sheets 1.0 (CSS1) standard, and was released on April 13, 2005. As with Acid1, an application passes the test if the way it displays the test page matches a reference image.

Acid2 tests aspects of HTML markup, CSS 2.1 styling, PNG images, and data URIs. The Acid2 test page will be displayed correctly in any application that follows the World Wide Web Consortium and Internet Engineering Task Force specifications for these technologies. These specifications are known as web standards because they describe how technologies used on the web are expected to function.

Acid2 was designed with Microsoft Internet Explorer particularly in mind. The creators of Acid2 were dismayed that Internet Explorer did not follow web standards. It was prone to display web pages differently from other browsers, causing web developers to spend time tweaking their web pages. Acid2 challenged Microsoft to make Internet Explorer comply with web standards.

Acid2 was released on April 13, 2005. On October 31, 2005, Safari 2.0.2 became the first browser to pass Acid2. Opera, Konqueror, Firefox, and others followed. With the release of Internet Explorer 8 on March 19, 2009, the latest versions of all major desktop web browsers now pass the test. Acid2 was followed by Acid3.


Acid2 was first proposed by Håkon Wium Lie, chief technical officer of Opera Software and creator of the widely used Cascading Style Sheets web standard.[1] In a March 16, 2005 article on CNET, Lie expressed dismay that Microsoft Internet Explorer did not properly support web standards and hence was not completely interoperable with other browsers. He announced that Acid2 would be a challenge to Microsoft to design Internet Explorer 7, then in development, to achieve a greater degree of standards compliance than previous versions of Internet Explorer. The original Acid1 test had forced browser makers to fix their applications or face embarrassment; Lie hoped that Acid2 would do the same.[2]

Lie and a colleague, Ian Hickson, had created the first draft of the test in February 2005.[3] Ian Hickson coded the final test in collaboration with the Web Standards Project and the larger web community.[2] [4] [5] [6] It was officially released on April 13, 2005[7] and at that time, every web browser failed it spectacularly.[8]

On April 23, 2005, Acid2 was updated to fix a bug that made the mouth appear too close to the nose.[9] [10] After several complaints, the test was again updated in January 2006 to remove a test for unpopular SGML-style comments that were never widely implemented. In browsers that do not implement SGML-style comments, the original test displayed the word "ERROR" on the bottom part of the face.[3]

In March 2008, Ian Hickson released Acid3 as a follow-up to Acid2. While Acid2 primarily tests CSS, Acid3 focuses more on JavaScript and other "Web 2.0" technologies.[11]

Microsoft's response

In July 2005, Chris Wilson, the Internet Explorer Platform Architect, stated that passing Acid2 was not a priority for Internet Explorer 7, describing the test as a "wish list" of features rather than a true test of standards compliance.[12] In December 2007, Microsoft announced that all the changes required to pass Acid2 would be made available in Internet Explorer 8, but that the changes would not be turned on by default, meaning that IE8 would not actually pass the test.[13] [14] The concern was that switching to a new behavior would cause too many problems in web pages expecting Internet Explorer's old, non-compliant behavior. Then in March 2008 Microsoft released IE8 beta 1 and turned on the changes by default after all.[15] James Pratt, Product Manager for IE8, explained that this decision was made so that "developers can spend more time building features and cool stuff, and less time just trying to tweak their sites across different browsers."[16]

Unfortunately, another unresolved standards compliance issue caused IE8 beta 1 to fail if not all elements of the test were hosted from the same server.[17] [18] In August 2008 Microsoft released IE8 beta 2, which resolved the issue.[19] As of that beta, however, standards mode is not turned on by default for pages loaded in the "Intranet Zone". This zone is active for pages loaded via UNC paths, named addresses without dots (like http://mysite/), and sites that bypass the proxy settings.[20] As such, IE8 will not pass the Acid2 test if loaded in these cases.[21]

Overview of standards tested

Acid2 tests a variety of web standards published by the World Wide Web Consortium and the Internet Engineering Task Force. With the exception of CSS 2.1, all web standards tested were codified before the year 2000.[22] [23] [24] [25] CSS 2.1 was a candidate recommendation at the time of Acid2's release,[26] and is still a candidate recommendation as of 23 April 2009.[27]

Specifically, Acid2 tests:[28]

Because Acid2 is not a comprehensive test, it does not guarantee total conformance to any particular standard. A variant of the Acid2 test that does not test for data URI support is also available from the Web Standards Project.[28]

Passing conditions

A passing score is only considered valid if the browser's default settings were used. Actions such as changing font sizes, zoom level, and applying user stylesheets can break the display of the test. This is expected and is not relevant to a browser's compliance.[38]

The following browser settings and user actions invalidate the test:[38] [39]

Compliant applications

If rendered correctly, Acid2 will appear as a smiley face below the text "Hello World!" in the user's browser, with the nose turning blue when the mouse cursor hovers over it. At the time of the test's release, every browser failed it,[8] but now a number of browsers pass it. See the list below.

Officially released

Non-compliant applications

Even though Opera Mini is based on the same rendering engine as Opera for personal computers, it does not pass the Acid2 test.[40] [41] This is because Opera Mini intentionally reformats web pages to try to make them more suitable for devices with small screens.[38] [42] [43]

Timeline of passing applications

The following is a list of releases noting significant releases of applications that passed the test. New applications that have passed Acid2 since their first official release are not included in the timeline.

27 April 2005Safariprivate build[44]
18 May 2005iCabprivate build[45] This build was made available to registered iCab users on May 20, 2005.
4 June 2005Konquerorprivate build[46]
6 June 2005iCabpublic buildWhether this version of iCab truly passes the test or not was questioned because it displays a scrollbar on the test page.[47] The CSS specification states that Acid2 correctly rendered should not have a scrollbar,[48] but also says that "there may exist valid reasons in particular circumstances" to ignore this requirement.[49] [50]
6 June 2005Safarisource code available[51] WebKit, the underpinnings of Safari, was made open source on June 6, 2005. When Safari was run with this latest version of WebKit, it passed the Acid2 test.
31 October 2005Safari 2.0.2official release[52] [53] Included in Mac OS X 10.4.3. First officially released web browser to pass test.
29 November 2005Konqueror 3.5official release[54] First Linux-compatible browser to pass the test, although it did not hide the scrollbar.
7 December 2005Prince 5.1official release[55] First non-web browser to pass test.
10 March 2006Opera 9 Development build 8249public weekly build[56] [57] First Microsoft Windows-compatible browser to pass the test and also the first Linux-compatible browser to pass the test including hiding the scrollbar. A public beta was released on April 20, also successful.[58] [59]
28 March 2006Konqueror 3.5.2official release[60] Updated to hide the scrollbar.[61] [62]
11 April 2006Mozilla Firefoxpublic nightly build[63] The "reflow refactoring" nightly builds, whose code was branched from the Gecko 1.9/Firefox 3.0 trunk, pass Acid2.
24 May 2006Opera Mobile for Symbian OSprivate build[64] First mobile browser to pass test.
20 July 2006OmniWeb 5.5 beta 1public build[65] [66] [67] OmniWeb switches its rendering engine to WebKit, the same rendering engine used in Safari which already passed the Acid2 test
20 June 2006Opera 9.0official release[68]
4 July 2006Obigo Browserprivate build[69] Second mobile browser to pass test.
17 August 2006iCab 3.0.3official release[70] First public release that hides the scrollbar.
6 September 2006OmniWeb 5.5official release
8 December 2006Mozilla Firefox, Camino, SeaMonkeypublic nightly build[71] Reflow refactoring branch is merged into main Gecko trunk. Firefox, Camino, and SeaMonkey trunk builds now pass Acid2.
5 March 2008Internet Explorer 8 Beta 1public build[72] Beta 1 passes the test when hosted at, but fails the test when hosted at or
17 June 2008Mozilla Firefox 3.0official release[73] [74]
27 August 2008Internet Explorer 8 Beta 2public build[75] Beta 2 and later pass the test unless it is hosted from the Intranet Zone.
2 September 2008Google Chrome 0.2 betapublic build[76]
14 October 2008Flock 2.0official release[77]
11 December 2008Google Chrome 1.0official release
19 March 2009Internet Explorer 8official release[78]
27 October 2009SeaMonkey 2.0official release[79]
18 November 2009Camino 2.0official release[80]
24 June 2010Spicebird 0.8official release[81]

See also

External links

Notes and References

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  2. Web site: The Acid2 challenge to Microsoft. Håkon Wium. Lie. Håkon Wium Lie. CNET. 16 March 2005. 12 January 2008.
  3. Web site: People who don't realise that they're wrong. Hickson. Ian. Ian Hickson. Hixie's Natural Log. 20 January 2006. 1 April 2008. 2 May 2008 . no.
  4. Web site: Ian Hickson. The Web Standards Project. 25 March 2008.
  5. Web site: Ben Henick. The Web Standards Project. 2 April 2008. 1 April 2008 . no.
  6. Web site: David Baron. The Web Standards Project. 2 April 2008.
  7. Acid2: Putting Browser Makers on Notice. The Web Standards Project. 13 April 2005. 1 April 2008.
  8. Web site: The Acid2 Test. Hyatt. Dave. Dave Hyatt. Surfin' Safari. MozillaZine. 12 April 2005. 1 April 2008. 31 March 2008 . no.
  9. Web site: Acid2: Version 1.1 Posted. Surfin' Safari. Hyatt. Dave. Dave Hyatt. MozillaZine. 23 April 2005. 24 December 2007. 23 December 2007 . no.
  10. Web site: Acid2: Lopping Off the Sideburns. Surfin' Safari. Hyatt. Dave. Dave Hyatt. MozillaZine. 20 April 2005. 14 May 2008. 14 May 2008 . no.
  11. Web site: Acid3 Browser Test. The Web Standards Project. 15 August 2008. 15 August 2008 . no.
  12. Web site: Standards and CSS in IE. Wilson. Chris. IEBlog. Microsoft. 29 July 2005. 11 March 2008. 15 March 2008 . no.
  13. Web site: IE 8: On the Path to Web Standards Compliance - ACID 2 Test Pass Complete. Charles. Microsoft. Microsoft Developer Network. 19 December 2007. 30 August 2008. About 19 minutes and 15 seconds through the video, Alex Mogilevsky, a member of the IE team, points at a picture of the Acid2 test improperly rendered and states "The video in the bottom is a IE7 version of smiley face...What you're looking at is actually IE8. It is what it looks currently in IE8 and it will look exactly like this when we ship IE8 because we are not breaking any compatibility, and this is a compatible mode of IE8. And, uh, most of the web relies on particular behavior including particular incorrect behavior, so the incorrect behavior will still be there unless the new content wants IE to be in standards-compliant mode, and then they will ask us, and then we will show perfectly standard picture.".
  14. Web site: Acid2 in IE8!. Håkon Wium. Lie. Håkon Wium Lie. Opera Software. 20 December 2007. 30 August 2008.
  15. Web site: Microsoft's Interoperability Principles and IE8. Hachamovitch. Dean. IEBlog. Microsoft. 3 March 2008. 30 August 2008. 30 August 2008 . no.
  16. Web site: IE8 Beta 2 screencast demo and interview. Tesar. David. Microsoft. 27 August 2008. 14 December 2008.
  17. Web site: Why Isn't IE8 Passing Acid2?. Microsoft. Phil. Nachreiner. 5 March 2008. 11 March 2008. 9 March 2008 . no.
  18. Web site: Re: MSIE 8 beta 1 clarification needed. Hickson. Ian. Ian Hickson. World Wide Web Consortium. 14 March 2008. 5 May 2008.
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  22. World Wide Web Consortium Issues First Recommendation for PNG. World Wide Web Consortium. 7 October 1996. 12 August 2008. 25 July 2008 . no.
  23. Web site: Cascading Style Sheets, level 2. Bos. Bert. Lie, Håkon Wium
    Lilley, Chris; Jacobs, Ian
    . World Wide Web Consortium. 11 April 2008. 12 August 2008. 11 August 2008 . no.
  24. Web site: RFC 2397 - The "data" URL scheme. Masinter, L. Internet Engineering Task Force. August. 1998. 12 August 2008. 15 September 2008 . no.
  25. Web site: HTML 4.01 Specification. Raggett. Dave. Dave Raggett. Le Hors. Arnaud. Jacobs. Ian. World Wide Web Consortium. 24 December 1999. 11 August 2008. 10 August 2008 . no.
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  27. Web site: Cascading Style Sheets, level 2 revision 1. Bos. Bert. Çelik, Tantek; Hickson, Ian; Lie, Håkon Wium. World Wide Web Consortium. 19 July 2007. 21 March 2009. 19 March 2009 . no.
  28. Web site: Acid2: The Guided Tour. The Web Standards Project. 24 December 2007. 23 December 2007 . no.
  29. Web site: Browser Stats. April. 2005. 23 August 2008. 13 August 2008 . no.
  30. Web site: Current Status of PNG. Roelofs. Greg. 14 March 2009. 4 April 2009. 13 April 2009 . no.
  31. Web site: HTML 4.0 Specification. Raggett. Dave. Dave Raggett. Arnaud Le. Hors. Jacobs. Ian. World Wide Web Consortium. 24 April 1998. 28 July 2008. 27 July 2008 . no.
  32. Web site: Proposed Standards. Official Internet Protocol Standards. Internet Society. 4 January 2009. 4 January 2009. 17 January 2009 . no.
  33. Web site: Objects, Images, and Applets: Rules for rendering objects. Raggett. Dave. Le Hors, Arnaud; Jacobs, Ian. HTML 4.01 Specification. W3C. 24 December 1999. 20 March 2008. 12 March 2008 . no.
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  35. Web site: Understanding CSS Positioning part 1. Valkhof. Kilian. 5 May 2008. 31 July 2008. 30 July 2008 . no.
  36. Web site: Box model. Cascading Style Sheets, level 2 revision 1. Bos. Bert. Çelik, Tantek; Hickson, Ian; Lie, Håkon Wium. World Wide Web Consortium. 19 July 2007. 5 January 2009. 5 January 2009 . no.
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  38. Web site: Acid2 and Opera 9 Clarifications: Yes, Opera 9 Passes the Test. Holzschlag, Molly E.. Molly Holzschlag. The Web Standards Project. 20 July 2006. 22 July 2006. 5 August 2006 . no.
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  40. Web site: Opera Mini 4 beta out. Bersvendsen. Arve. June. 2007. 22 December 2007.
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  46. Web site: Konqueror now passes Acid2. Sandfeld, Allan [carewolf]. carewolf's blog. KDE Developer's Journals. 4 June 2005. 16 May 2006. 14 June 2006 . no.
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  57. Web site: …and one more weekly!. Santambrogio. Claudio. 10 March 2006. 10 May 2008.
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  64. Web site: Opera for Symbian passes Acid2. Nevstad. Magnus. The Digital Void of SPZ. Opera Software. 24 May 2006.
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  80. Web site: Camino 2 Release Notes.
  81. Web site: Spicebird 0.8 Release Notes.