Clarify use of context-locals with signals.

Author: rduplain

docs/signals.rst

@@ -131,6 +131,8 @@ debugging.  You can access the name of the signal with the
    missing blinker installations, you can do so by using the
    :class:`flask.signals.Namespace` class.
 
+.. _signals-sending:
+
 Sending Signals
 ---------------
 
@@ -156,6 +158,17 @@ function, you can pass ``current_app._get_current_object()`` as sender.
    that :data:`~flask.current_app` is a proxy and not the real application
    object.
 
+
+Signals and Flask's Request Context
+-----------------------------------
+
+Signals fully support :ref:`reqcontext` when receiving signals.  Context-local
+variables are consistently available between :data:`~flask.request_started` and
+:data:`~flask.request_finished`, so you can rely on :class:`flask.g` and others
+as needed.  Note the limitations described in :ref:`signals-sending` and the
+:data:`~flask.request_tearing_down` signal.
+
+
 Decorator Based Signal Subscriptions
 ------------------------------------