cim20.dtd

Document Type Definition Reference

A .dtd file contains a Document Type Definition. The definition declares the permitted elements, attributes, and entities of an XML or SGML document. A parser validates a document against the DTD. The newer XML Schema format covers the same task with more data types. DTD syntax comes from the SGML standard.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.