DITA specializations often rely on Document Type Definitions (DTDs) or XML Schemas for validation. Here’s an explanation of their role:

DTDs and Schemas: DTDs or XML Schemas provide the formal structure and constraints for DITA documents. They define the elements, attributes, and their relationships within DITA topics. This ensures that DITA content adheres to a predefined structure, including any custom elements introduced in specializations.

Validation: When content is authored or edited, DTDs or Schemas are used for validation. Validation tools and authoring environments check the content against these definitions to confirm that it complies with the DITA standards and any customization rules introduced through specializations.

Custom Elements and Attributes: Organizations can define custom elements and attributes within DTDs or Schemas for their DITA specializations. These customizations are incorporated into the validation process, ensuring that content with specializations is both consistent and compliant with the organization’s requirements.

Compliance: By using DTDs or Schemas, organizations can enforce compliance with their specialization rules and DITA standards. This validation mechanism helps maintain the integrity and consistency of the specialized content.

Example:

An organization specializing DITA for product documentation introduces a custom element <custom-specification> to describe product specifications. This element is defined within the DTD or Schema, and content using it must conform to this structure:

<!-- DTD definition with custom DITA specialization for product specifications -->
<!ELEMENT custom-specification (spec-title, spec-description)>
<!ELEMENT spec-title (#PCDATA)>
<!ELEMENT spec-description (#PCDATA)>