Base DITA includes the topic, map elements, metadata, classification, and specialization
  elements. It also includes domains for hazard statement, typographic, and utility
  elements
  The base section of the architectural specification contains the following parts:
    - An introduction, which provides background concepts and an overview of the architecture
 
    - The DITA markup section, which provides an overview of DITA topics, DITA maps, and DITA
     metadata
 
    - The DITA processing section, which provides descriptions of common DITA-processing
     expectations
 
    - The configuration, specialization, and constraints section, which provides
     details of the mechanisms that DITA provides for defining, extending, and constraining DITA
     document types