anchor.diff:  * <<constant-keyword,`constant_keyword`>>
   * <<text,`text`>> field with a <<keyword,`keyword`>> or
     <<constant-keyword,`constant_keyword`>> sub-field
  -
  -<<array,Array values>> are not supported.
   --
   
   `<greedy_matching>`::
  
positive.code: * <<constant-keyword,`constant_keyword`>>
  * <<text,`text`>> field with a <<keyword,`keyword`>> or
    <<constant-keyword,`constant_keyword`>> sub-field
  
  <<array,Array values>> are not supported.
  --
  
  `<right>`::
  
negative.code: * <<constant-keyword,`constant_keyword`>>
  * <<text,`text`>> field with a <<keyword,`keyword`>> or
    <<constant-keyword,`constant_keyword`>> sub-field
  --
  
  *Returns:* integer or `null`
  