anchor.diff:  The basic example above declares a new rule named `cc`, along with the
   command to run.  (In the context of a rule, the `command` key is
   special and defines the command to run.  A full list of special keys
  -is provided in the reference.)
  +is provided in <<ref_rule,the reference>>.)
   
   Variables begin with a `$` and are described more fully later, but
   here `$in` expands to the list of input files (`foo.c`) and `$out` to
  
positive.code: 
  Rule variables
  ~~~~~~~~~~~~~~
  
  A `rule` block contains a list of `key = value` declarations that
  affect the processing of the rule.  Here is a full list of special
  
negative.code: where `target` is a known output described by `build.ninja` in the
  current directory.
  
  
  Creating .ninja files
  ~~~~~~~~~~~~~~~~~~~~~
  Here's a basic `.ninja` file that demonstrates most of the syntax.
  
  ---------------------------------
  