Today I converted an ASP.NET 2.0 webapplication to 4.0 using Visual Studio 2010 RC.  The convert process ran quite smoothly. After the conversion I discovered two new attributes in the pages tag of the converted web.config file, curious?

1. controlRenderingCompatibilityVersion="3.5"

Default HTML rendering of web server controls will be according the rendering of the controls in the version 3.5 of the .NET framework.  The minimum value of this attribute is 3.5. More info on MSDN

2. clientIDMode="AutoID"

ASP.NET 4.0 gives the power to control how id’s are generated in the rendered HTML of web server controls. And that is a good thing. For compatibility reasons it’s set to AutoID here so it will be the same as always. More info on MSDN