docs: Add MLS presentation language to `Proposal`.
@@ -90,6 +90,23 @@ impl TryFrom<u16> for ProposalType {
/// Proposal.
///
/// This `enum` contains the different proposals in its variants.
+///
+/// ```c
+/// // draft-ietf-mls-protocol-16
+///
+/// struct {
+/// ProposalType msg_type;
+/// select (Proposal.msg_type) {
+/// case add: Add;
+/// case update: Update;
+/// case remove: Remove;
+/// case psk: PreSharedKey;
+/// case reinit: ReInit;
+/// case external_init: ExternalInit;
+/// case group_context_extensions: GroupContextExtensions;
+/// };
+/// } Proposal;
+/// ```
#[allow(clippy::large_enum_variant)]
#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
#[allow(missing_docs)]
