W3CDTD
W3CDTD is a term used to refer to the set of document type definitions published by the World Wide Web Consortium (W3C) to specify the grammar and structure of markup languages such as HTML and XHTML. A DTD defines the allowed element names, attributes, entities, and the relationships between elements, enabling software to validate a document’s conformance to a given markup vocabulary.
Historically, W3C DTDs were central to validating HTML 4.01 and XHTML 1.x documents. Examples include the HTML
In modern web development, HTML5 has largely moved away from DTDs in favor of a parsing algorithm