Modular design
 
  - Schemas are about elements and attributes named by qualified names:
   
    - A pair of namespace name and local name.
 
- A schema may include components for multiple namespaces.
- Schema documents are primarily about one namespace.
- But you can assemble multiple schema documents to build a single schema:
    
    - include a schema document for the same namespace;
- import a schema for another namespace.