PEP 553 is now final.

Also, document the behavior of $PYTHONBREAKPOINT under -E

pep-0553.rst

@@ -1,7 +1,7 @@
 PEP: 553
 Title: Built-in breakpoint()
 Author: Barry Warsaw <barry@python.org>
-Status: Accepted
+Status: Final
 Type: Standards Track
 Content-Type: text/x-rst
 Created: 2017-09-05
@@ -150,7 +150,13 @@ If access to the ``PYTHONBREAKPOINT`` callable fails in any way (e.g. the
 import fails, or the resulting module does not contain the callable), a
 ``RuntimeWarning`` is issued, and no breakpoint function is called.
 
-
+Note that as with all other ``PYTHON*`` environment variables,
+``PYTHONBREAKPOINT`` is ignored when the interpreter is started with
+``-E``.  This means the default behavior will occur
+(i.e. ``pdb.set_trace()`` will run).  There was some discussion about
+alternatively treating ``PYTHONBREAKPOINT=0`` when ``-E`` as in
+effect, but the opinions were inconclusive, so it was decided that
+this wasn't special enough for a special case.
 
 
 Implementation