DOCUMENT TYPE DEFINITION:
A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines the document structure with a list of legal elements and attributes.
A DTD can be declared inline inside an XML document, or as an external reference.

Internal DTD Declaration:
If the DTD is declared inside the XML file, it should be wrapped in a DOCTYPE definition with the following syntax:


External DTD Declaration:
If the DTD is declared in an external file, it should be wrapped in a DOCTYPE definition with the following syntax: