DTD is an acronym for Document Type Definition. Files that contain the .dtd file extension are text files that specify certain elements that are used in an SGML, HTML, XHTML or XML document.
The information that is contained in the DTD files is used to define the structure of given XML data. This data may define the order and nesting of a document's elements and attributes, which are referenced within a web page. The DTD file allows a computer that is receiving XML from another computer to agree on the structure of the XML data that is being transmitted, ensuring uniformity.
The DTD file can also be used to determine whether or not a file represents a valid document.
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File.org aims to be the go-to resource for file type- and related software information. We spend countless hours researching various file formats and software that can open, convert, create or otherwise work with those files.
If you have additional information about the DTD file format or software that uses files with the DTD suffix, please do get in touch - we would love hearing from you.