It's a nice time saver if you would like the HTML editor to automatically add quotes for the attribute values while you are typing. To set this option select Tools->Options. Check Show all settings. From the left pane select Text Editor -> HTML
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Read the complete post at http://blogs.iis.net/webdevelopertips/archive/2009/05/29/tip-66-did-you-know-how-to-insert-quotes-values-automatically-while-typing-the-attrib-values.aspx