What are the limitations of a DTD ?

In addition to Document Type Definitions, schema supports data type definitions too. Xml 1.0 does not provide option to use namespace in DTD's, whereas scienc provides. DTD provide structure for xml documents.
Limits identified with DTD help. Imperatives with respect to XML instances which are not checked:.
Substance Name: a trait worth about kind substance or substances must match the name about a unparsed substance proclaimed in the DTD.