Key parts of a DTD

The DTD references a root element, which is the overall keyword that categorizes all the data to be contained in the XML elements. Technically, the XML file will specify the root element, but the DTD should reference a root element in an opening comment for clarity to users of the DTD.

Each element must be declared (defined) in order to establish what kind of content information it can contain. If an element can contain child elements (subelements of the parent element), those child elements must be listed in the declaration of the parent element. The parent element is a container element, and child elements are nested under the parent element on the XML Tree on the XML Workspace palette.