How do we set DotNetNuke to use XHTML 1.0 transitional DTD?
DotNetNuke only uses one page to present its content. This page is the default.aspx page that is in the root of your DotNetNuke installation files. In order to set DNN to specify XHTML 1.0 Transitional as the Document Type Definition (DTD) we need to edit the default.aspx page. Note: From DotNetNuke version 4.4+ you can now change the DOC TYPE directly within a skin. This is outlined in this tutorial: How to select DOC TYPES in DotNetNuke 4.4 Before editing the default.aspx page, make sure you read this tutorial in full to ensure you are aware of the pros and cons of changing the default.aspx page.