[pep8] Document empty blocks

pep-0008.txt

@@ -310,6 +310,18 @@ Note, some editors and web-based code viewers may not recognize
 control-L as a form feed and will show another glyph in its place.
 
 
+Empty blocks
+------------
+
+Use ``pass`` to denote a block is intentionally empty.  In empty
+class or function bodies, prefer a meaningful docstring instead of
+``pass``.
+
+Do not use ``...`` or ``None`` for this purpose.  The former suggests
+"details supressed" instead of "there is nothing there".  The latter
+looks like an unfinished thought.
+
+
 Source File Encoding
 --------------------
 
@@ -642,6 +654,7 @@ Other Recommendations
 
       if foo == 'blah': one(); two(); three()
 
+
 When to Use Trailing Commas
 ===========================