diff --git a/docs/interop.md b/docs/interop.md
index 930e6dc..07fa420 100644
--- a/docs/interop.md
+++ b/docs/interop.md
@@ -5,6 +5,7 @@ for that certain considerations are taken:
 * number of public api calls is kept at the minimum
 * procedure parameters can only use basic types, no aggregates, with exception of Vec/Matrix types and alike,
   with no new additions, ever (see [/include/twn_types.h](../include/twn_types.h))
+* enum types are allowed, as they decay to numeric type (but language-specific api can decide to provide simple ways to use them)
 * optionals can be expressed via pointer passage of value primitives, assumed immutable, with the NULL expressing default value
 * no opaque types, only keys if needed
 * pointers to pointers aren't allowed
@@ -15,3 +16,4 @@ for that certain considerations are taken:
 * 32 bit floating point is the only numeric type
 * [/include/twn_api.json](../share/twn_api.json) file is hand-kept with a schema to aid automatic binding generation and tooling
 * parameter names should not collide with keywords of any language that is targetted; if so happens, parameter alias could be added
+* any procedure can't have more than 8 parameters