Support legacy portions along with PEP 420 portions.

pep-0420.txt

@@ -38,6 +38,8 @@ Within this PEP:
    stored in a zip file) that contribute to a namespace package.
  * "regular package" refers to packages as they are implemented in
    Python 3.2 and earlier.
+ * "legacy portion" refers to a portion that uses ``__path__``
+   manipulation in order to implement namespace packages.
 
 This PEP defines a new type of package, the "namespace package".
 
@@ -184,6 +186,11 @@ be empty) is added to the list of recorded path entries and path
 searching continues.  If ``loader`` is not ``None``, it is immediately
 used to load a module or regular package.
 
+Even if ``loader`` is returned and is not ``None``,
+``<iterable-of-path-entries>`` must still contain the path entries for
+the package.  This allows code such as ``pkgutil.extend_path()`` to
+compute path entries for packages that it does not load.
+
 Note that multiple path entries per finder are allowed.  This is to
 support the case where a finder discovers multiple namespace portions
 for a given ``fullname``.  Many finders will support only a single
@@ -230,6 +237,18 @@ any standard library packages become namespace packages is outside the
 scope of this PEP.
 
 
+Migrating from legacy namespace packages
+----------------------------------------
+
+As described above, prior to this PEP ``pkgutil.extend_path()`` was
+used by legacy portions to create namespace packages.  Because it is
+likely not practical for all existing portions of a namespace package
+to be migrated to this PEP at once, ``extend_path()`` will be modified
+to also recognize PEP 420 namespace packages.  This will allow some
+portions of a namespace to be legacty portions while others are
+migrated to PEP 420.
+
+
 Packaging Implications
 ======================