Document why we wrap it in the view, not the context

lib/python/Products/Five/browser/providerexpression.py

@@ -41,6 +41,8 @@ class Z2ProviderExpression(StringExpr):
         if provider is None:
             raise cp_interfaces.ContentProviderLookupError(name)
 
+        # A content provider's context (__parent__) is the view, not
+        # the context object.
         if getattr(provider, '__of__', None) is not None:
             provider = provider.__of__(view)