Internet Explorer 8 was released on March 19, 2009. It had been in development since August 2007 at the latest. On March 5, 2008, the first public beta (Beta 1) was released to the general public. On August 27, 2008, the second public beta (Beta 2) was released. It is supported in Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista, Windows 7, and Windows Server 2008 on both 32-bit as well as 64-bit architectures. Internet Explorer 8 (IE8) RC1 was released on January 26, 2009. Internet Explorer 8 "Final" was released on March 19, 2009. Security, ease of use, and improvements in RSS, CSS, and Ajax support are Microsoft's priorities for IE8. It includes much stricter compliance with web standards, including a planned full Cascading Style Sheets 2.1 compliance for the release version. All these changes allow Internet Explorer 8 to pass the Acid2 test. However, to prevent compatibility issues, IE8 also includes the IE7 rendering behavior. Sites that expect IE7 quirks can disable IE8's breaking changes by including a meta element in the HEAD section of the HTML document. IE8 also includes numerous improvements to JavaScript support as well as performance improvements, although it still does not pass the Acid3 test, with version 8.0 scoring 20/100. It includes support for "Accelerators" - which allow supported web applications to be invoked without explicitly navigating to them - and "WebSlices" - which allows portions of page to be subscribed to and monitored from a redesigned "Favorites Bar". Other features include "InPrivate" privacy features and SmartScreen phishing filter.