diff --git a/mercurial/bundlerepo.py b/mercurial/bundlerepo.py
--- a/mercurial/bundlerepo.py
+++ b/mercurial/bundlerepo.py
@@ -346,6 +346,7 @@ class bundlerepository(localrepo.localre
 def instance(ui, path, create):
     if create:
         raise util.Abort(_('cannot create new bundle repository'))
+    # internal config: bundle.mainreporoot
     parentpath = ui.config("bundle", "mainreporoot", "")
     if not parentpath:
         # try to find the correct path to the working directory repo