anchor.diff:  `Defines`, and so on.
   
   .Native Unit Propagate synopsis
  +[source,lua]
   ---------------------------------------------------
   <unit type> {
       ...
  
positive.code: - Run the project's +tundra.lua+ script to set options
  - Load toolsets, syntax files and other information as required by the configuration script
  - Run the referred +Units+ file (or function) in syntax mode to define the project's build units
  - Parse the resulting declarations and generate DAG nodes
  - Pass the DAG to the native build engine for building
  
  == The tundra.lua file ==
  
negative.code: build for that configuration, such as include paths, libraries and so on.
  
  .Config Synopsis
  [source,lua]
  -------------------------------------------------------------------------------
  Config {
      -- Required
  