/// Ed448 contexts as used by Ed448ph.
///
/// Contexts are domain separator strings that can be used to isolate uses of
/// the algorithm between different protocols (which is very hard to reliably do
/// otherwise) and between different uses within the same protocol.
///
/// To create a context, call either of the following:
///
/// - [`SigningKey::with_context`](crate::SigningKey::with_context)
/// - [`VerifyingKey::with_context`](crate::VerifyingKey::with_context)