When you set a breakpoint in your .aspx page like above, VS 2008 will automatically map the breakpoint location to the dynamically generated client HTML that runs in the browser when the page is later executed:
If you add/remove/update the breakpoint locations in the running HTML document, VS 2008 is also now smart enough to perform the reverse mapping and update the breakpoint in the original .aspx or .master source file on the server. This makes it much easier to get into a nice edit/debug/edit/debug flow as you are iterating on your applications.
Script Document Navigation within the Solution Explorer
VS 2008 makes it much easier to-do this by integrating the running Script Document feature (that in VS 2005 was a separate tool-pane window) into the VS 2008 solution explorer view when you are debugging a web application.
Specifically, when you are using VS to run and debug a page, VS 2008 will now list all of the script URLs that the page you are debugging has loaded in the browser at the top of your VS solution explorer pane:
Much Richer Debug Watch/Locals and Visualizer Support
You can now browse runtime object methods:
You can now browse runtime object events:
And you now get much, much more detailed property and property type information of running objects. Note below how I am traversing the div element's "parentElement" property to dynamically look up details about the element's parent HTML element and overall position within the HTML DOM:
Hope this helps,