DTD

A DTD (Document Type Definition) is the structure-definition mechanism of XML 1.0; it is simpler than XSD but limited, and is written in a special (non-XML) syntax.

Purpose

To provide basic structural validation for XML, defining the allowed elements, attributes, and hierarchy.

Mechanism

<!ELEMENT name (content)> declares elements and children, <!ATTLIST> declares attributes, and <!ENTITY> declares entities. There is no type system (strings only) and no namespaces. Before HTML5, HTML used a DTD.

Use cases

HTML 4.01 / XHTML 1.0 DTDs
Legacy XML document validation
SVG 1.1 DTD
Teaching examples

Examples

Input

<!ELEMENT name (#PCDATA)>

Output

The name element contains text only

Element declaration

Common errors

A DTD cannot express modern constraints (types, namespaces): Migrate to XSD or JSON Schema

Related terms

XSD (XML Schema Definition) is the W3C-standard language for defining XML document structure, describing elements, attributes, and type constraints in XML syntax.

XML (Extensible Markup Language) is the W3C-standard markup language describing data with a tag tree, supporting namespaces, schema validation, and style transformation.

JSON Schema is a vocabulary for describing the structure of JSON documents, defining types, constraints, and validation rules; it is the schema standard for JSON.

References