Explicitly specify binary encoding for string truncation

index.bs

@@ -3194,7 +3194,7 @@ associated with or [=scoped=] to, respectively.
 
         When [=clients=], [=client platforms=], or [=authenticators=] display a {{PublicKeyCredentialEntity/name}}'s value, they should always use UI elements to provide a clear boundary around the displayed value, and not allow overflow into other elements [[css-overflow-3]].
 
-        Authenticators MAY truncate a {{PublicKeyCredentialEntity/name}} member's value so that it fits within 64 bytes, if the authenticator stores the value. See [[#sctn-strings-truncation]] about truncation and other considerations.
+        Authenticators MAY truncate a {{PublicKeyCredentialEntity/name}} member's value so that its UTF-8 encoding fits within 64 bytes, if the authenticator stores the value. See [[#sctn-strings-truncation]] about truncation and other considerations.
 </div>
 
 
@@ -3265,8 +3265,9 @@ credential.
 
         When [=clients=], [=client platforms=], or [=authenticators=] display a {{PublicKeyCredentialUserEntity/displayName}}'s value, they should always use UI elements to provide a clear boundary around the displayed value, and not allow overflow into other elements [[css-overflow-3]].
 
-        [=Authenticators=] MUST accept and store a 64-byte minimum length for a {{PublicKeyCredentialUserEntity/displayName}}
-        member's value. Authenticators MAY truncate a {{PublicKeyCredentialUserEntity/displayName}} member's value so that it fits within 64 bytes. See [[#sctn-strings-truncation]] about truncation and other considerations.
+        [=Authenticators=] MUST accept and store a {{PublicKeyCredentialUserEntity/displayName}} member's value
+        whose UTF-8 encoding is 64 bytes or shorter.
+        Authenticators MAY truncate a {{PublicKeyCredentialUserEntity/displayName}} member's value so that its UTF-8 encoding fits within 64 bytes. See [[#sctn-strings-truncation]] about truncation and other considerations.
 </div>