Update section on impact to finders.

pep-0420.txt

@@ -144,7 +144,14 @@ deferred until a sub-level import occurs.
 Impact on Import Finders and Loaders
 ------------------------------------
 
-To be determined in the sample implementation.
+PEP 302 defines "finders" that are called to search path
+elements. These finders' ``find_module`` methods currently return
+either a "loader" object or None. For a finder to contribute to
+namespace packages, ``find_module`` will return a third type: a
+string. This is the string that will be recorded and later used as a
+component of the namespace module's __path__, as described above.
+
+[Consider Brett's idea to pass NamespaceLoader in to PathFinder]
 
 Discussion
 ==========