Question

what is the extension name of DTD​

Answer 1

Document type definition. A document type definition (DTD) is a set of markup declarations that define a document type for an SGML-family markup language (SGML, XML, HTML). A DTD defines the valid building blocks of an XML document.

Answer 2

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Document type definition. A document type definition (DTD) is a set of markup declarations that define a document type for an SGML-family markup language (SGML, XML, HTML). A DTD defines the valid building blocks of an XML document.