updated explanation of 'pyin' messages

docs/source/development/messaging.rst

@@ -395,6 +395,8 b' the outcome. See :ref:`below <execution_results>` for the possible return'
 codes and associated data.
 
 
+.. _execution_counter:
+
 Execution counter (old prompt number)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -403,7 +405,7 b' requests that are made with ``store_history=True``. This counter is used to pop'
 the ``In[n]``, ``Out[n]`` and ``_n`` variables, so clients will likely want to
 display it in some form to the user, which will typically (but not necessarily)
 be done in the prompts.  The value of this counter will be returned as the
-``execution_count`` field of all ``execute_reply`` messages.
+``execution_count`` field of all ``execute_reply`` and ``pyin`` messages.
 
 .. _execution_results:
 
@@ -906,7 +908,10 b' to update a single namespace with subsequent results.'
 Python inputs
 -------------
 
-These messages are the re-broadcast of the ``execute_request``.
+To let all frontends know what code is being executed at any given time, these
+messages contain a re-broadcast of the ``code`` portion of an
+:ref:`execute_request <execute>`, along with the :ref:`execution_count
+<execution_counter>`.
 
 Message type: ``pyin``::