docs/uselect: Describe more aspects of poll.register/modify behavior.
E.g., register() can be called again for the same object, while modify()
will raise exception if object was not register()ed before.
@@ -45,13 +45,18 @@ Methods
*eventmask* defaults to ``uselect.POLLIN | uselect.POLLOUT``.
+ It is OK to call this function multiple times for the same *obj*.
+ Successive calls will update *obj*'s eventmask to the value of
+ *eventmask* (i.e. will behave as `modify()`).
+
.. method:: poll.unregister(obj)
Unregister *obj* from polling.
.. method:: poll.modify(obj, eventmask)
- Modify the *eventmask* for *obj*.
+ Modify the *eventmask* for *obj*. If *obj* is not registered, `OSError`
+ is raised with error of ENOENT.
.. method:: poll.poll(timeout=-1)
