diff -r a63af1c8e0b1 Doc/library/allos.rst
--- a/Doc/library/allos.rst	Sat Oct 12 19:54:30 2013 +0200
+++ b/Doc/library/allos.rst	Sat Oct 12 20:32:02 2013 +0200
@@ -28,3 +28,16 @@ but they are available on most other sys
    platform.rst
    errno.rst
    ctypes.rst
+
+
+.. _availability:
+
+Notes on availability
+=====================
+
+* An "Availability: Unix" note means that this function is commonly found on
+  Unix systems.  It does not make any claims about its existence on a specific
+  operating system.
+
+* If not separately noted, all functions that claim "Availability: Unix" are
+  supported on Mac OS X, which builds on a Unix core.
diff -r a63af1c8e0b1 Doc/library/os.rst
--- a/Doc/library/os.rst	Sat Oct 12 19:54:30 2013 +0200
+++ b/Doc/library/os.rst	Sat Oct 12 20:32:02 2013 +0200
@@ -29,15 +29,6 @@ Notes on the availability of these funct
   objects, and result in an object of the same type, if a path or file name is
   returned.
 
-* An "Availability: Unix" note means that this function is commonly found on
-  Unix systems.  It does not make any claims about its existence on a specific
-  operating system.
-
-* If not separately noted, all functions that claim "Availability: Unix" are
-  supported on Mac OS X, which builds on a Unix core.
-
-.. Availability notes get their own line and occur at the end of the function
-.. documentation.
 
 .. note::
 
@@ -100,7 +91,7 @@ process and user.
 
    Return the filename corresponding to the controlling terminal of the process.
 
-   Availability: Unix.
+   .. availability:: Unix
 
 
 .. data:: environ
@@ -193,7 +184,7 @@ process and user.
    and ``'surrogateescape'`` error handler. Use :func:`os.getenvb` if you
    would like to use a different encoding.
 
-   Availability: most flavors of Unix, Windows.
+   .. availability:: most flavors of Unix, Windows
 
 
 .. function:: getenvb(key, default=None)
@@ -201,7 +192,7 @@ process and user.
    Return the value of the environment variable *key* if it exists, or
    *default* if it doesn't. *key*, *default* and the result are bytes.
 
-   Availability: most flavors of Unix.
+   .. availability:: most flavors of Unix
 
    .. versionadded:: 3.2
 
diff -r a63af1c8e0b1 Doc/tools/sphinxext/pyspecific.py
--- a/Doc/tools/sphinxext/pyspecific.py	Sat Oct 12 19:54:30 2013 +0200
+++ b/Doc/tools/sphinxext/pyspecific.py	Sat Oct 12 20:32:02 2013 +0200
@@ -5,7 +5,7 @@
 
     Sphinx extension with Python doc-specific markup.
 
-    :copyright: 2008, 2009, 2010, 2011, 2012 by Georg Brandl.
+    :copyright: 2008-2013 by Georg Brandl.
     :license: Python license.
 """
 
@@ -113,6 +113,27 @@ class ImplementationDetail(Directive):
         return [pnode]
 
 
+# Support for documenting platform availability
+
+class Availability(Directive):
+
+    has_content = False
+    required_arguments = 1
+    optional_arguments = 0
+    final_argument_whitespace = True
+    has_content = False
+
+    def run(self):
+        pnode = nodes.paragraph(classes=['availability'])
+        n, m = self.state.inline_text(':ref:`Availability <availability>`: ',
+                                      self.lineno)
+        pnode.extend(n + m)
+        n, m = self.state.inline_text(self.arguments[0], self.lineno)
+        pnode.extend(n + m)
+        pnode += nodes.Text('.', '.')
+        return [pnode]
+
+
 # Support for documenting decorators
 
 from sphinx import addnodes
@@ -336,6 +357,7 @@ def setup(app):
     app.add_role('issue', issue_role)
     app.add_role('source', source_role)
     app.add_directive('impl-detail', ImplementationDetail)
+    app.add_directive('availability', Availability)
     app.add_directive('deprecated-removed', DeprecatedRemoved)
     app.add_builder(PydocTopicsBuilder)
     app.add_builder(suspicious.CheckSuspiciousMarkupBuilder)