The <DOCTYPE> statement and <head> (including required and optional metadata) are provided in the "XHTML Module Template" as are some of the basic DKN "tokens". Save the template so that it can be reused. When you are creating a module with an html editor, you may copy and paste the <DOCTYPE> statement and <head> from the template into an existing valid xhtml file, or, alternatively, you may use the template and copy or enter the content into the template. When using this approach, do not "Save", use "Save As" so that the template is not altered. The metadata, including name of author, dates, etc. in the <head> will need to be changed to reflect the details for the module being authored. The DKN xhtml master template is available at: xhtml Master Template.