Examine and Resolve XHTML Compliance Issues

By default, Visual Studio 2005 generates and validates XHTML-compliant markup. This helps you build Web applications that are standards compliant and helps minimize issues with browser-specific rendering. Visual Studio .NET 2003 did not generate XHTML-compliant markup, so you might see validation and rendering issues with pages created in Visual Studio .NET 2003.

Note: Validation errors are informational only and are flagged as warnings. Validation errors do not prevent a page from running.

If you do not want to see validation errors, switch the HTML validation setting from XHTML Transitional to Internet Explorer 6.0 (which was the Visual Studio .NET 2003 default setting). In the Tools menu, click Options. In the Options dialog box, open the Text Editor node, then the HTML node, and then the Validation node. In the Target list, select Internet Explorer 6.0, and then unselect the Show Errors check box. Note that this does not fix XHTML validation errors; it simply switches the validation schema to one that is more compatible with the way markup was generated by Visual Studio .NET 2003, and it suppresses validation warnings.

You also can add the following section to your project's Web.config file, which causes ASP.NET to render legacy (non-XHTML compliant) markup from server controls:

<system.Web>
   <xhtmlConformance mode="Legacy" />
</system.Web>

This will avoid the slight rendering differences you might see between pages displayed using ASP.NET 1.1 and using ASP.NET 2.0. For more information, see ASP.NET and XHTML in the MSDN Library.