File "w47_ppwarning.ml", line 10, characters 12-25:
10 | let x1 = 42 [@@ppwarning]
                 ^^^^^^^^^^^^^
Warning 47 [attribute-payload]: illegal payload for attribute ppwarning.
  A single string literal is expected

File "w47_ppwarning.ml", line 13, characters 12-37:
13 | let x2 = 42 [@@ppwarning "foo" "bar"]
                 ^^^^^^^^^^^^^^^^^^^^^^^^^
Warning 47 [attribute-payload]: illegal payload for attribute ppwarning.
  A single string literal is expected

File "w47_ppwarning.ml", line 16, characters 12-28:
16 | let x3 = 42 [@@ppwarning 84]
                 ^^^^^^^^^^^^^^^^
Warning 47 [attribute-payload]: illegal payload for attribute ppwarning.
  A single string literal is expected

File "w47_ppwarning.ml", line 19, characters 25-30:
19 | let x4 = 42 [@@ppwarning "foo"]
                              ^^^^^
Warning 22 [preprocessor]: foo