What is DTD

What is DTD?
A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines rules for a specific type of document, including:

• Names of elements, and how and where they can be used
• The order of elements
• Proper nesting and containment of elements
• Element attributes

To apply a DTD to an XML document, you can:

• Include the DTD's element definitions within the XML document itself.
• Provide the DTD as a separate file, whose name you reference in the XML document.