diff --git a/bsip-0040.md b/bsip-0040.md
index 2d27915..a62ba5f 100644
--- a/bsip-0040.md
+++ b/bsip-0040.md
@@ -82,6 +82,7 @@ List of possible asserts are:
 | `length`      | [`min`, `max`] | stateless |
 | `limit` | [`max_cumsum`, `interval_in_sec`]      | [`current_cumsum`, `interval_began`] |
 | `limit_monthly` | [`max_cumsum`, `interval_in_months`]      | [`current_cumsum`, `interval_began`] |
+| `contains` | [`list`, `of`, `allowed`, `fields`] | stateless |
 
 All asserts apply to `int`, `string` and `object_ids`. There is no type converstion, incompatible type means assert failure. Any more sophisticated data types are not included yet.
 
@@ -111,6 +112,9 @@ 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.
+
 ### Simple Example
 Assume account A and B and some unrelated key K. Furthermore A has a custom active authority in the following way:
 ```