Tip #76: Did you know… How to hide a non-visual control in your designer?
Some times as you are building your web page, you may want to hide all the non-visual controls like Timer control so that the page looks close to how it would be rendered on your browser. Our Designer can toggle between displaying and not displaying Non
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Read the complete post at http://blogs.msdn.com/webdevelopertips/archive/2009/06/09/tip-76-did-you-know-how-to-hide-a-non-visual-control-in-your-designer.aspx