Specialization in design enables reuse of design elements, just
as specialization in content allows reuse of processing rules. These rules
involve the creation and management of markup modules as separate reusable
units.
Why specialization in design?
Following the rules for specialization design enables reuse of design elements, just as following the rules for specialized content enables reuse of content
Modularization and integration of design
Specialization hierarchies are implemented as sets of module files that declare the markup and entities that are unique to each specialization. The modules must be integrated into a document type before they can be used.