Acid3

Acid3 is a test page from the Web Standards Project that checks how well a web browser follows certain web standards, especially relating to the Document Object Model and JavaScript.

When successful, the Acid3 test displays a gradually increasing percentage counter with colored rectangles in the background. The percentage displayed is based on the number of sub-tests passed. In addition to these the browser also has to render the page exactly like the reference page as rendered in the same browser. Like the text of the Acid2 test the text of the reference rendering is not a bitmap in order to allow for certain differences in font rendering.

Acid3 was in development from April 2007, and released on 3 March 2008. The main developer was Ian Hickson, who also wrote the Acid2 test. Acid2 focused primarily on Cascading Style Sheets, but this third Acid test focuses also on technologies used on modern, highly interactive websites characteristic of Web 2.0, such as ECMAScript and DOM Level 2. A few tests also concern Scalable Vector Graphics (SVG), XML and data: URIs. It includes several elements from W3C CSS3 working drafts that have not made it to candidate recommendations yet.

Name

Acid3 is a short for "Acid test #3". During the the gold rush of the 1850s, an acid test was a test designed to testify whether a given (excavated or found) metal is indeed gold.

Acid test was "the" test of the time, since it was decisive, immediate, cheap and extremely simple to perform. An analogy is drawn from this historical test to the modern test - if a browser passes the acid test it is approved, very much in the same manner that if a metal passes the acid test it is accepted.

The test

The main part of Acid3 is written in ECMAScript (JavaScript) and consists of 100 subtests in six groups called "buckets", including four special tests (0, 97, 98, and 99).

• Bucket 1: DOM Traversal, DOM Range, []
• Bucket 2: DOM2 Core and DOM2 Events
• Bucket 3: DOM2 Views, DOM2 Style, CSS 3 selectors and Media Queries
• Bucket 4: Behavior of HTML tables and forms when manipulated by script and DOM2 HTML
• Bucket 5: Tests from the Acid3 Competition (SVG, HTML, SMIL, Unicode, …)
• Bucket 6: ECMAScript

The compliance criteria requires that the test is run with a browser's default settings. The final rendering must have a 100/100 score and must not only be pixel-identical with the reference rendering, including the favicon (or more accurately, its desired absence; a favicon is not supposed to show up in a 100/100 render), but the animation has to be smooth (taking no more than 33 ms for each subtest on the top-of-the-line Apple laptop) as well.

As the test is run, rectangles are added to the rendered image; the color of the rectangles is decided by the number of sub-tests passed in the bucket. If all subtests fail in a particular bucket, its associated rendered rectangle will be invisible. If some subtests are cleared the color will change in four steps:

• 1-5 subtests passed: Black rectangle.
• 6-10 subtests passed: Grey rectangle.
• 11-15 subtests passed: Silver rectangle.
• All 16 subtests passed: Colored rectangle (red, orange, yellow, lime, blue, purple - for each of the six rectangles, respectively).

After the Acid3 test page is completely rendered, the capital A in the word Acid3 can be clicked to see an alert (or Shift-Click for a new window) explaining exactly which subtests have failed, and what the error message was.

In order to render the test correctly, user agents need to implement the CSS 3 Text Shadows and the CSS 2.x Downloadable Fonts specifications, which are currently under consideration by W3C to be standardized. This is required as the test uses a custom TrueType font, called "AcidAhemTest" to cover up an "X" on fuchsia colored background. The glyph, when rendered by the downloaded font, is just a square, made white with CSS, and thus invisible.

In addition, the test also uses Base64 encoded images, some more advanced selectors, CSS 3 color values (HSLA) as well as bogus selectors and values that should be ignored.

Development and impact

Ian Hickson started working on the test in April 2007, but development progressed slowly. In December 2007, work restarted and the project received public attention on 10 January 2008, when it was mentioned in blogs by Anne van Kesteren and Dustin Brewer. At the time the project resided at a URL clearly showing its experimental nature: "http://www.hixie.ch/tests/evil/acid/003/NOT_READY_PLEASE_DO_NOT_USE.html" That did not stop the test from receiving widespread attention within the web development community. At that time only 84 subtests were done, and on 14 January Ian Hickson announced a competition to develop the missing 16.

The following developers contributed to the final test through this competition:

• Sylvain Pasche. Test 66–67 (DOM).
• David Chan. Test 68 (UTF-16/UCS-2).
• Simon Pieters (Opera) and Anne van Kesteren (Opera). Test 71: HTML parsing.
• Jonas Sicking (Mozilla) and Garrett Smith. Test 72: dynamic modification of style blocks' text nodes.
• Jonas Sicking (Mozilla). Test 73: Nested events.
• Erik Dahlström (Opera). Test 74–78: SVG and SMIL.
• Cameron McCormack. Test 79: SVG fonts.

Even before its official release, Acid3's impact on browser development was dramatic. WebKit in particular made progress; in less than a month their score rose from 60 to 87.

The test was officially released on March 3, 2008. A guide and commentary was expected to follow within a few months, however, as of September 2008 it has not yet been released. The announcement that the test is complete means only that it is to be considered "stable enough" for actual use; if problems and bugs are found, it will still be modified to fix it. The test has already been modified to fix several issues including issues regarding to sub-pixel positioning, SVG surrogate pairs and performance. On March 26, 2008—the day both Opera and WebKit teams announced a 100/100 score—developers of WebKit contacted main Acid3 developer Ian Hickson about a critical bug in the Acid3 that presumably may have forced a violation of the SVG 1.1 standard to pass; thus Hickson proceeded to fix it with the help of Cameron McCormack, member of W3C's SVG Working Group.

By the end of March 2008, early development versions of the Presto and WebKit layout engines scored 100/100 on the test and rendered the test page correctly. Presto still has performance issues in producing a smooth animation in the test, thus it has not passed the Acid3 test yet. As of build r36882, WebKit produces a smooth animation on the reference hardware, and thus passes the Acid3 test. Firefox developers had been preparing for the imminent release of Firefox 3, as a result they had focused on stability rather than passing the Acid3 test. Microsoft, developers of the Internet Explorer browser, said that Acid3 does not map to the goal of Internet Explorer 8 and that IE8 will improve only some of the standards being tested by Acid3.

On April 22, 2008, Hickson again fixed a bug in the Acid3 test discovered by a Mozilla developer. This change possibly invalidates the previously reported scores of 100/100 for development versions of Presto and WebKit. On September 29, 2008, David Baron raised an issue with the CSS Working Group concerning media queries that might cause the test to change again.

Layout engines

Acid3 was deliberately written in such a way that every web browser failed the test at the time of its release. Many of the browser teams are actively working to improve test results.

Desktop browsers

Desktop layout engine progress for the Acid3 test

Layout Engine	Major Browsers	Screen­shot of Stable Build at Time of Acid3 Release	Latest Stable Build Screen­shot	De­vel­op­ment Build Screen­shot	Not­es
Gecko	Firefox, Flock	052/100 Firefox 2.0.0.12	071/100 Firefox 3.0.3	097/100 Gecko/try-836bb85189e Minefield/3.1b1pre
KHTML	Konqueror	061/100 Konqueror 4.0.2	077/100 Konqueror 4.1.2	078/100 Konqueror snapshot r816030
Presto	Opera	046/100 Opera 9.25	085/100 Opera 9.60	099/100 WinGogi Acid3 build
Trident	Internet Explorer	014/100 IE 7.0	014/100 IE 7.0	021/100 IE 8.0 Beta2
WebKit	Safari, Google Chrome, Omni­Web, Midori	041/100 Safari 3.0.4	075/100 Safari 3.1.2	100/100 Safari 4 Developer Preview, also Chromium (Google Chrome) build 2778	.

Mobile browsers

Mobile layout engine progress for the Acid3 test

Layout Engine	Major Browsers	Screen­shot of Stable Build at Time of Acid3 Release	Latest Stable Build Screen­shot	De­vel­op­ment Build Screen­shot	Not­es
Gecko	Fennec			088/100
Presto in Opera Mini	Opera Mini		080/100 Opera Mini 4.1.1.11320
Presto	Opera Mobile	002/100 Opera Mobile 8.65	002/100 Opera Mobile 8.65	071/100 Opera Mobile 9.51
NetFront	NetFront		011/100 NetFront 3.5
WebKit	Mobile­Safari	040/100 iPhone firmware 1.1.4	074/100 iPhone firmware 2.1

See also

• Comparison of layout engines

References

External links

• The Acid3 Test
• The Acid3 Test (Reference Rendering)
• The Acid3 test at Web Standards Project
• Post-release revisions to the Acid3 test