DTD coding requirements

DITA coding practices for DTDs rely heavily on entities to implement specialization and constrraints. As such, an understanding of entities is critical when working with DTD document-type shells, vocabulary modules, or constraint modules.

A DTD-based document-type shell is organized into sections; each section contains entity declarations that follow specific coding rules.

This topic covers general coding requirements for defining element types in both structural and element-domain vocabulary modules. In addition, it covers how to create the @domains attribute contribution for these modules.

A structural vocabulary module defines a new topic or map type as a specialization of a topic or map type.

The vocabulary modules that define element domains have an additional coding requirement. The entity declaration file must include a parameter entity for each element that the domain extends.

The vocabulary modules that define attribute domains have additional coding requirements. The module must include a parameter entity for the new attribute, which can be referenced in document-type shells, as well as a text entity that specifies the contribution to the @domains attribute for the attribute domain.

A structural constraint module defines the constraints for a map or topic element type. A domain constraint module defines the constraints for an element or attribute domain.