anchor.diff:  ;
   alternativeTypeList : (namedType) (COMMA namedType)*
   ;
  -namedType : IDENTIFIER   type
  +namedType : IDENTIFIER   asnType
   ;
   enumeratedType : ENUMERATED_LITERAL L_BRACE enumerations R_BRACE
   ;
  
positive.code: 
  typeFieldSpec : AMPERSAND IDENTIFIER typeOptionalitySpec?
  ;
  typeOptionalitySpec : OPTIONAL_LITERAL | (DEFAULT_LITERAL type)
  ;
  fixedTypeValueFieldSpec : AMPERSAND IDENTIFIER type UNIQUE_LITERAL? valueOptionalitySpec ?
  ;
  valueOptionalitySpec : OPTIONAL_LITERAL | (DEFAULT_LITERAL value)
  ;
  
negative.code: 
  
  contentsConstraint :
     CONTAINING_LITERAL asnType
   |  ENCODED_LITERAL BY_LITERAL value
   |  CONTAINING_LITERAL asnType ENCODED_LITERAL BY_LITERAL value
  ;
  
  
  