4.1 Introduction
 4.2 Project file structure
  4.2.1 The options node
  4.2.2 The option node
  4.2.3 The packages node
  4.2.4 The package node
  4.2.5 The units node
  4.2.6 The unit node
  4.2.7 The descriptions node
  4.2.8 The description node
  4.2.9 The imports node
  4.2.10 The import node