I enjoyed reading Tips and Tricks from ScottGu's Blog, it is really interesting. Try to find out more detail from his blog.
Tip/Trick: Using Server Side Comments with ASP.NET 2.0
You are coding away on an ASP.NET page, and are trying to isolate a problem within the page. You have some existing html/controls/markup/in-line code that is being used on the page, and you want to temporarily comment it out while you fix the problem.
ASP.NET supports a little known feature called “server-side comments” that you can use to completely disable code/controls/html in a page. Server-side comments in ASP.NET are delimited using a <%-- --%> syntax.
For more info for this tip : http://weblogs.asp.net/scottgu/archive/2006/07/09/Tip_2F00_Trick_3A00_-Using-Server-Side-Comments-with-ASP.NET-2.0-.aspx
For more Information on lots of coding tricks log to ScottGu's Blog : http://weblogs.asp.net/scottgu/pages/ASP.NET-2.0-Tips_2C00_-Tricks_2C00_-Recipes-and-Gotchas.aspx