The Acid test is a test, developed by the Web Standards Project (WaSP), to test whether a browser complies with web standards. Web standards are developed and maintained by the World Wide Web Consortium (W3C); the W3C was founded by the inventor of the World Wide Web: Tim Berners-Lee. The purpose of W3C: is to maintain a standard version of web technologies like: HTML and CSS. These web technologies dictate how webpages are designed and displayed. Browsers are client programs that retrieve webpages from the Internet and render them using the specifications - of HTML and CSS - outlined by the W3C.
The problem is that some browsers do not adhere to web standards, and display HTML and CSS differently to browsers that do comply with web standards. This creates a problem for web developers: as their website may not render correctly in each browser and it may 'cost' them visitors due to a lack of compatibility with the browser a user has installed. The Web Standards Project (WaSP) is a group that attempts to 'force' browser developers into adhere to web standards by testing their browser compatibility with web standards and publishing the results. The tests that the WaSP use are the: Acid1, Acid2, Acid3 and Acid4 Tests. These tests primarily test the following:
However, the Acid tests also test: HTTP Protocol, DOM Levels, ECMAScript, CSS Selectors, Unicode 5.0 UTF-16, Unicode 5.0 UTF-8, SVG 1.1, SVG 1.1 Fonts and XHTML 1.0.