A DTD-syntax topic specialization module consists of two files: a .ent file that defines entities used to integrate the module into document type shell DTDs, and a .mod file that declares the element types. Starting with DITA 1.2 structural modules should provide
@domains attribute declarations.
For XSD-based structural modules there are two XSD documents: a *Grp.xsd that defines groups used to integrate the module into document type shell XSDs, and a *Mod.xsd that declares the element types and attributes for the module.
For example, if your specializations require a specific formatting effect that is not the default DITA behavior for the base types, you must extend the output processors you use to provide the formatting effect. Typically this means creating extension XSLT scripts for use with the DITA Open Toolkit, but it can also mean extending built-in editor configurations and style sheets, or extending or customizing content management systems, Web sites, and so on, depending on the nature of the specialization.