anchor.diff:      | '#' 
       | LIDENTIFIER 
       | UIDENTIFIER 
  -    | specialValue 
  +    | selfReference 
       | nonstringLiteral
       | prefixOperator
       ;
  
positive.code:     : '$' | '-' |'++' | '--' | '~'
      ;
  
  specialValue
      : 'this' 
      | 'super'
      ;
  
  enumeration
  
negative.code: 
  THIS
      :   'this'
      ;
  
  OUTER
      :   'outer'
      ;
  
  SUBTYPE
  