anchor.diff:  
       rule expression: expr<<[]>>
   
  -    rule function_name: VAR
  -        | function_operator
  +    rule function_name: VAR | function_operator
   
       rule function_operator:
           TOKOPPLUS | TOKOPMINUS | TOKOPSTAR
  
positive.code:     rule function_header:
          FUNCTION
          [
              ( Type_item_or_name_sub
              | LPAREN Type_item_or_name RPAREN
              )
          ]
          [function_name]
  
negative.code:     rule interface_declaration:
          TOKINTERFACE [VAR [COLONCOLON VAR] [VAR]]
          ( [ SEMICOLON ] interface_body
          | interfaceTypesub SEMICOLON interface_body
          | EQUAL assign_value SEMICOLON
          )
  
  