DTD stands for Document Type Definition. DTD defines the structure, elements and attributes of an XML document. Document Type Definition forms like the structure of the tree and describes something about its data. Document Type Definition (DTD) consists of SGML family structure, like GML, SGML, HTML, XML. In this case, it’s XML.
A DTD can be declared inline or as an external recommendation within an XML document. The DTD specifies how many times a node should appear and how their child nodes should be ordered.
PCDATA and CDATA are the two data types.
* PCDATA is character data that has been parsed.
* CDATA is character data that is not typically parsed.
