Oh, yeah, maybe it's the `rust` or maybe its the `~~~`  (most tests use 

    ```

)

But if you put a `fn main() {}` in the test somewhere, rustdoc will no longer automatically insert the wrapping function main, so I think

```rust
#[feature(phase)];
#[phase(syntax)] extern crate collections;

/* bitset!() declaration */

fn main() {
    let e1 = FlagA | FlagC;
    // etc.
}
```

might work.