
`is_placeholder`, despite having an "is_" name, actually returns an int: 1 for `_1`, 2 for `_2`, 3 for `_3`, and so on. But it should still be int, not size_t.
`is_placeholder`, despite having an "is_" name, actually returns an int: 1 for `_1`, 2 for `_2`, 3 for `_3`, and so on. But it should still be int, not size_t.