Direct Link from the ECM and SharePoint Team Blogs:
The AspMenu class that ships with WSS 3.0 (and by extension MOSS 2007) is nearly identical in behavior to ASP.NET 2.0’s Menu class (as the name implies). AspMenu derives from Menu and adds tweaks to work around a few reasonably well known annoyances and provides improved highlighting support.
Unfortunately, this class was marked sealed and is therefore not eligible to be used as the base class for derived types. Effectively, this means that customers cannot inherit the additional functionality of the AspMenu class when trying to provide further customization of the menu.
We realized this problem too late in the release process and were unable to remove the sealed marker from the AspMenu class that ships with WSS. However, we are instead providing the source code for that class here (as an attachment to this blog entry) under the name MossMenu.
Issues with the ASP.NET 2.0 menu, which have been worked around:
1) If the mouse pointer happens to be hovering over a menu item that exposes a fly-out as the page is loading, it is possible that an error dialog will appear stating: “Internet Explorer cannot open the Internet site, Operation aborted” and a blank page will be shown upon clicking OK. It seems that the problem arises from attempting to append to the DOM before it is properly initialized.
2) If SSL termination is employed on a site with a menu, users will be greeted with “This page contains both secure and nonsecure items. Do you want to display the nonsecure items?” when hovering over a menu item which exposes fly-outs. (http://support.microsoft.com/?id=910444)
3) In right-to-left locales, the fly-out indicator arrow still points from left-to-right.
Improvements to default highlighting behavior of ASP.NET 2.0 menu:
· When hooking the menu up to a SiteMapProvider through a SiteMapDataSource, the menu automatically highlights the node that matches that returned by the provider’s CurrentNode property. However, if the particular node returned by CurrentNode is not shown by the menu nothing will be highlighted at all. The improved behavior determines if there is an ancestor of the current node which is displayed in the menu and highlights this node instead.Download the ASPMenu Source