anchor.diff:  
   subscript
       : ELLIPSIS
  -    | test
  -    | test? COLON test? sliceop?
  +    | test (COLON test? sliceop?)?
  +    | COLON test? sliceop?
       ;
   
   // TODO: maybe inline?
  
positive.code: // Python 2 : EXCEPT test COMMA name
  // Python 3 : EXCEPT test AS name
  except_clause
      : EXCEPT (test (COMMA name | AS name)?)? COLON suite
      ;
  //----------------------------------------------------------------------------------------------------------------------
  
  
negative.code: // TODO 2: semantically annotated declaration is not an assignment
  small_stmt
      : testlist_star_expr assign_part?                                                 #expr_stmt
      | {CheckVersion(2)}? PRINT ((test (COMMA test)* COMMA?)
                         | RIGHT_SHIFT test ((COMMA test)+ COMMA?)) {SetVersion(2);}    #print_stmt   // Python 2
      | DEL exprlist                                                                    #del_stmt
      | PASS                                                                            #pass_stmt
      | BREAK                                                                           #break_stmt
  