Remove responsibility mixup

Fixes #16.

Author: kelunik

META.md

@@ -22,4 +22,8 @@ Even though we are not using a thenable, `Promise` is a more recognizable and ac
 
 ## Creation of Promises
 
-Promise creation and managing is out of scope of this specification, as managing never shall cross library boundaries and thus does not need to be interoperable at all; each library shall resolve the Promise it created itself.
+`Promise` creation and managing is out of scope of this specification, as managing never shall cross library boundaries and thus does not need to be interoperable at all. Each library shall resolve the `Promise` it created itself.
+
+## Resolution of Promises
+
+The specification defines that the value of a `Promise` must never be another `Promise`. Implementations may still accept to be resolved by a promise and then defer the resolution until the passed promise resolves.

README.md

@@ -19,7 +19,7 @@ For further design explanations and notes, please refer to [the meta document](M
 ## Terminology
 
 1. _Promise_ is an object implementing `Interop\Async\Promise` and conforming to this specification.
-2. _Value_ is any legal PHP value (including `null`), except an instance of `Interop\Async\Promise`.
+2. _Value_ is any legal PHP value (including `null`), but not an instance of `Interop\Async\Promise`.
 3. _Error_ is any value that can be thrown using the `throw` statement.
 4. _Reason_ is an error indicating why a `Promise` has failed.
 
@@ -74,8 +74,6 @@ Any implementation MUST at least provide these two parameters. The implementatio
 
 All registered callbacks MUST be executed in the order they were registered. If one of the callbacks throws an `Exception` or `Throwable`, it MUST be forwarded to `Async\Interop\Promise\ErrorHandler::notify`. The `Promise` implementation MUST then continue to call the remaining callbacks with the original parameters.
 
-If a `Promise` is resolved with another `Promise`, the `Promise` MUST keep in pending state until the passed `Promise` is resolved. Thus, the value of a `Promise` can never be a `Promise`.
-
 ## Contributors
 
 * [Aaron Piotrowski](https://github.com/trowski)