message: Document trait sealing
diff: @@ -259,6 +259,11 @@ mod sealed {
  }
  /// Output from a successful `command` syscall.
  +///
  +/// This trait is [sealed], meaning foreign implementations cannot be defined,
  +/// even though it can be referenced by foreign crates.
  +///
  +/// [sealed]: https://rust-lang.github.io/api-guidelines/future-proofing.html#sealed-traits-protect-against-downstream-implementations-c-sealed
  pub trait SuccessData: sealed::Sealed {
  /// The return variant for this success type, stored in `r0` after
  /// performing a `command` syscall.
  @@ -316,6 +321,11 @@ impl SuccessData for (u32, u32, u32) {
  }
  /// Output from a failed `command` syscall.
  +///
  +/// This trait is [sealed], meaning foreign implementations cannot be defined,
  +/// even though it can be referenced by foreign crates.
  +///
  +/// [sealed]: https://rust-lang.github.io/api-guidelines/future-proofing.html#sealed-traits-protect-against-downstream-implementations-c-sealed
  pub unsafe trait FailureData: sealed::Sealed {
  /// The return variant for this failure type, stored in `r0` after
  /// performing a `command` syscall.
  