diff --git a/bsip-0040.md b/bsip-0040.md
index fd7df57..fff721a 100644
--- a/bsip-0040.md
+++ b/bsip-0040.md
@@ -81,11 +81,11 @@ List of possible asserts are:
 | `lt, le, gt, ge`      | `comparative` | stateless |
 | `limit` | [`max_cumsum`, `interval_in_sec`]      | [`current_cumsum`, `interval_began`] |
 | `limit_monthly` | [`max_cumsum`, `interval_in_months`]      | [`current_cumsum`, `interval_began`] |
-| `contains_only` | [`list`, `of`, `allowed`, `fields`] | stateless |
+| `may_mutate` | `attribute_to_assert` = [{`attribute_identifier`: `any of above assert_objects`}] | stateless |
 
 There is no implicit type conversion when attempting to assert, incompatible type means assert failure.
 
-In the following we list possible `asserts`. Mentioning `argument value` refers to the value of the argument of the operation specified `argument` in `assert_object`.
+In the following we list possible `asserts`. Mentioning `argument value` refers to the value of the argument of the operation specified `argument` in `assert_object`. The logic does not differentiate if an `argument` is optional or mandatory. All asserts imply: If the `argument` is given, it must pass the `assert`. If the `argument` is not given, assert is implicitly passed.
 
 #### `any`
 Stateless assert, all argument types. `Argument value` must be equal to one of values in the data list
@@ -113,8 +113,11 @@ The assert that needs to pass is now `current_cumsum + incoming value <= max_cum
 #### `limit_monthly`
 Statefull assert, only `int` type arguments. Analogue to `limit`, but `interval_began` is initially set to `month(valid_from)` and set to `month(now)` on update, additionally the time assert is `month(now) >= interval_began + interval_in_months` (include logic for month overflow when year changes).
 
-#### `contains_only`
-Stateless assert, only for dictionary type objects like `options`. The `argument` of the operation is a dictionary type objects and is only allowed to contain the attributes in the data list.
+#### `attribute_assert`
+Stateless assert, only for dictionary type objects. The `attribute_to_assert` list contains mappings between attributes and asserts that they must fulfill, if present in the dictionary.
+
+Note:
+- Assume `asset_update_operation`. All attributes of its `options` must be filled on update call. This assert can not be used to realize a "may only change attribute xzy of `options`". This would require that the logic knows which of the arguments are reflected on-chain and it knows how to query it for every operation that contains `options`. If `options` are to be restricted with this assert, all values that should not change would need be fixated by defining a `any` assert for those attributes, while having e.g. a `lt` assert for the one attribute that is allowed to change.
 
 #### Example: Simple transfer
 Assume account A and B and some unrelated key K. Furthermore A has a custom active authority in the following way: