anchor.diff:  
   Ninja file reference
   --------------------
  +
   A file is a series of declarations.  A declaration can be one of:
   
   1. A rule declaration, which begins with +rule _rulename_+, and
  
positive.code: 
  4. Variables from the file that included that file using the
     `subninja` keyword.
  
negative.code: where `target` is a known output described by `build.ninja` in the
  current directory.
  
  There is no installation step; the only files of interest to a user
  are the resulting binary and this manual.
  
  
  Creating .ninja files
  