Add multi unlock tx validity

tips/TIP-0052/tip-0052.md

@@ -212,9 +212,16 @@ A Multi Address is only valid if all of the following conditions hold:
 A Multi Unlock is only valid if all of the following conditions hold:
 
 - `2 <= Unlocks Count <= 10`.
-- If `Unlocks` contains Reference, Account or NFT Unlocks, they must point to an Unlock outside of the Multi Unlock.
-- Whenever a _Multi Unlock_ is present in a transaction, the uniqueness of _Signature Unlocks_ must be validated across
-  all present _Signature Unlocks_, in particular also those contained in _Multi Unlocks_.
+
+A transaction containing a Multi Unlock is only valid if all of the following conditions hold:
+
+- If the transaction's `Unlocks` field contains Reference, Account, Anchor or NFT Unlocks, they must point to an Unlock
+  outside of the Multi Unlock.
+- The _Multi Unlock_ must be unique within the subset of _Multi Unlocks_ in the `Unlocks` field of the transaction based
+  on the serialization of the unlock.
+- Any _Signer UIDs_ from _Signature Unlocks_ present in a _Multi Unlock_ are not also present outside a multi unlock.
+  - Note that this implies that duplicate _Signature Unlocks_ are allowed to be present within multiple distinct Multi
+    Unlocks.
 
 #### Additional semantic transaction validation rules