anchor.diff:          TOKCASE paren_expression
           ( TOKMATCHES
             (
  -              ( dot_field_selection
  -              | LBRACE tagged_dot_list (COMMA tagged_dot_list)* RBRACE
  -              | TOKDEFAULT
  -              | VAR 
  -              )
  +              matches_clause
                 COLON (QUESTION SEMICOLON | single_statement)
             )*
           | (
  
positive.code:     rule param_list:
          LPAREN [ assign_rvalue (COMMA assign_rvalue)* ] RPAREN
  
  ##########
  ########## Statements
  ##########
  
      rule declared_item:
          term<<[]>> [ assign_opvalue ]
  
      rule variable_declaration_or_call:
          ( Type_item declared_item ( COMMA declared_item )*
          | expr<<[]>> [   ( declared_item ( COMMA declared_item )*
                           | assign_opvalue
                           )
  
negative.code:         |  TOKAMPERAMPERAMPER  nterm<<V>>
          |  TOKBAR  nterm<<V>>
          |  TOKBARBAR  nterm<<V>>
          |  TOKMATCHES matches_clause
          |  TOKPERCENT  nterm<<V>>
          )*  {{ return v }}
  
  