History support on Microsoft Ajax Library 3.5 SP1

The history control maintain the browser back button. An explanation of the feature is located in the Readme documentation of the Microsoft Ajax Library 3.5 SP1 package.
For quick reference the links are listed below:

• Managing Browser History Using Client Script: http://msdn.microsoft.com/en-us/library/cc488538.aspx
• Sys.Application.addHistoryPoint: http://msdn.microsoft.com/en-us/library/cc488025.aspx
• Sys.Application.navigate event: http://msdn.microsoft.com/en-us/library/cc488024.aspx

In order to allow the browser history feature without using the server-side ScriptManager control, it is necessary to add the following markup into the page for Internet Explorer versions before 8:

<iframe id="__historyFrame" src="/System.Web.Extensions/3.5.0.0/3.5.30729.1/empty.htm" style="display:none;"></iframe>