add comments

common/djangoapps/static_replace/__init__.py

@@ -87,11 +87,15 @@ def replace_static_urls(text, data_directory, course_namespace=None):
         # In debug mode, if we can find the url as is,
         if settings.DEBUG and finders.find(rest, True):
             return original
-        # course_namespace is not None, then use studio style urls
+        # if we're running with a MongoBacked store course_namespace is not None, then use studio style urls
         elif  course_namespace is not None and not isinstance(modulestore(), XMLModuleStore):
+            # first look in the static file pipeline and see if we are trying to reference
+            # a piece of static content which is in the mitx repo (e.g. JS associated with an xmodule)
             if staticfiles_storage.exists(rest):
                 url = staticfiles_storage.url(rest)
             else:
+                # if not, then assume it's courseware specific content and then look in the
+                # Mongo-backed database
                 url = StaticContent.convert_legacy_static_url(rest, course_namespace)
         # Otherwise, look the file up in staticfiles_storage, and append the data directory if needed
         else: