anchor.diff:  
   value
     : STRING
  -  | NUMBER
  +  | (REAL_OR_EXPONENT_NUMBER | SIGNED_INT)
     | object
     | array
     | 'true'
  
positive.code:   : [0-9a-fA-F]
    ;
  
  NUMBER
    : '-'? INT '.' [0-9] + EXP?
    | '-'? INT EXP
    | '-'? INT
    ;
  
  fragment INT
    : '0'
  
negative.code: 
  literal : '`' value '`' ;
  
  DIGIT : [0-9] ;
  
  LETTER : [a-zA-Z] ;
  