SEP-44: Minor edits to undefine the fourth event topic

ecosystem/sep-0044.md

@@ -7,8 +7,8 @@ Authors: Leigh McCulloch <@leighmcculloch>
 Track: Standard
 Status: Draft
 Created: 2024-08-26
-Updated: 2024-09-05
-Version 0.2.0
+Updated: 2024-09-09
+Version 0.2.1
 Discussion: TBA
 ```
 
@@ -43,11 +43,10 @@ pub trait TokenExtMemoInterface {
     /// # Events
     ///
     /// Emits an event with:
-    /// - topics - `["transfer", from: Address, to: Address, _: Val, memo: u64]`
+    /// - topics - `["transfer", from: Address, to: Address, _: _, memo: u64]`
     /// - data - `amount: i128`
-    /// The events fourth topic can be any Val as defined by other standards or
-    /// custom contract behavior. If the contract does not currently emit any
-    /// value in the fourth topic field, it can simply emit `()`, the Void Val.
+    /// The events fourth topic is undefined. If the contract does not otherwise
+    /// emit a value in the fourth topic field, it can emit `()`, the Void Val.
     fn transfer_memo(env: Env, from: Address, to: Address, amount: i128, memo: u64);
 }
 ```
@@ -64,7 +63,7 @@ The event has topics:
 - `Symbol` with value `"transfer"`
 - `Address` the address holding the balance of tokens that was drawn from.
 - `Address` the address that received the tokens.
-- `Val` any value the token already emits as the fourth topic.
+- `_` undefined and contracts should otherwise emit whatever they would normally emit for this field, or `()` / Void.
 - `u64` the memo.
 
 The event has data:
@@ -74,25 +73,27 @@ The event has data:
 ## Design Rationale
 
 There are a variety of ways that memos could be introduced into either the Stellar protocol or the contract transfer
-protocol. Adding a new function that accepts the memo parameter is the simplest and least ambiguous.
+protocol. Adding a new function that accepts the memo parameter is the least ambiguous.
 
 Given that [CAP-27] introduced muxed accounts for non-contract operations it is worth noting why support for muxed
 accounts are not being proposed. Memos, and muxed IDs, primarily exist to support offchain protocols, but adding support
-for a muxed account or address type to Soroban would make it extremely easy for existing contracts to store balances
-against the muxed account instead of the underlying account.
+for a muxed account or address type to Soroban's Address type would make it extremely easy for existing contracts to
+store balances against the muxed account instead of the underlying account.
 
 The memo is limited to the `u64` type because previous research on the topic when [CAP-27] was proposed found that most
-uses of memos were integers, or were compatible with integers.
+impactful non-advertising uses of memos were integers, or were compatible with integers. At anytime a future SEP could
+expand the types suppored by the memo field if that became necessary.
 
 The [SEP-41] `transfer` event is reused and extended rather than a new event introduced because [SEP-41] uses the
 `transfer` event for all account to account transfers and while possible it seems best to continue to emit the same
 event in the new case which is really only an annotation. One challenge is that the [CAP-46-6] implementation of
 [SEP-41] already extended the `transfer` event topic list. For this reason the fourth field of the event topic list is
-assumed present with any value as defined by the token contract or other standards and this proposal has no opinion of
-its type and purpose. The memo is expected in the fifth field.
+assumed present with any value as defined by the token contract or other standards and this proposal leaves it undefined
+and has no opinion of its type and purpose. The memo is expected in the fifth field.
 
 ## Changelog
 
+- `v0.2.1` - Minor edits to undefine the fourth event topic.
 - `v0.2.0` - Move memo into fifth event topic field in SEP-44 and CAP-61.
 - `v0.1.0` - Initial draft.