diff --git a/mercurial/httpconnection.py b/mercurial/httpconnection.py
--- a/mercurial/httpconnection.py
+++ b/mercurial/httpconnection.py
@@ -126,6 +126,7 @@ class http2handler(urllib2.HTTPHandler, 
         self.ui = ui
         self.pwmgr = pwmgr
         self._connections = {}
+        # developer config: ui.http2debuglevel
         loglevel = ui.config('ui', 'http2debuglevel', default=None)
         if loglevel and not _configuredlogging:
             _configuredlogging = True
diff --git a/mercurial/url.py b/mercurial/url.py
--- a/mercurial/url.py
+++ b/mercurial/url.py
@@ -469,6 +469,7 @@ def opener(ui, authinfo=None):
     construct an opener suitable for urllib2
     authinfo will be added to the password manager
     '''
+    # experimental config: ui.usehttp2
     if ui.configbool('ui', 'usehttp2', False):
         handlers = [httpconnectionmod.http2handler(ui, passwordmgr(ui))]
     else: