pep-567: More fixes (#504)

pep-0567.rst

@@ -16,7 +16,7 @@ Abstract
 
 This PEP proposes a new ``contextvars`` module and a set of new
 CPython C APIs to support context variables.  This concept is
-similar to thread-local variables, but, unlike TLS, it allows
+similar to thread-local storage (TLS), but, unlike TLS, it allows
 correctly keeping track of values per asynchronous task, e.g.
 ``asyncio.Task``.
 
@@ -136,11 +136,11 @@ restore the ``ContextVar`` to its previous value, or remove it from
 the context if it was not set before.  The ``ContextVar.reset(Token)``
 is used for that::
 
-    old = var.set(1)
+    token = var.set(1)
     try:
         ...
     finally:
-        var.reset(old)
+        var.reset(token)
 
 The ``Token`` API exists to make the current proposal forward
 compatible with :pep:`550`, in case there is demand to support
@@ -155,7 +155,7 @@ like ``decimal`` and ``numpy``.
 contextvars.Context
 -------------------
 
-``Context`` objects are mappings of ``ContextVar`` to values.
+``Context`` object is a mapping of context variables to values.
 
 To get the current ``Context`` for the current OS thread, use
 the ``contextvars.get_context()`` method::
@@ -180,9 +180,12 @@ be contained in the ``ctx`` context::
         assert var.get() == 'ham'
 
     ctx = get_context()
+
+    # Any changes that 'function' makes to 'var' will stay
+    # isolated in the 'ctx'.
     ctx.run(function)
 
-    assert var.get('spam')
+    assert var.get() == 'spam'
 
 Any changes to the context will be contained and persisted in the
 ``Context`` object on which ``run()`` is called on.
@@ -218,8 +221,9 @@ keyword-only argument, which defaults to the current context::
         # ... some time later
         context.run(callback, *args)
 
-Tasks in asyncio need to maintain their own isolated context.
-``asyncio.Task`` is modified as follows::
+Tasks in asyncio need to maintain their own isolated context that
+they inherit from the point they were created at.  ``asyncio.Task``
+is modified as follows::
 
     class Task:
         def __init__(self, coro):
@@ -378,6 +382,22 @@ points to a ``_ContextData`` object::
             self.__used = False
 
 
+Summary of the New APIs
+=======================
+
+* A new ``contextvars`` module with ``ContextVar``, ``Context``,
+  and ``Token`` classes, and a ``get_context()`` function.
+
+* ``asyncio.Loop.call_at()``, ``asyncio.Loop.call_later()``,
+  ``asyncio.Loop.call_soon()``, and
+  ``asyncio.Future.add_done_callback()`` run callback functions in
+  the context they were called in.  A new *context* keyword-only
+  parameter can be used to specify a custom context.
+
+* ``asyncio.Task`` is modified internally to maintain its own
+  isolated context.
+
+
 Backwards Compatibility
 =======================