diff --git a/mercurial/namespaces.py b/mercurial/namespaces.py
new file mode 100644
--- /dev/null
+++ b/mercurial/namespaces.py
@@ -0,0 +1,25 @@
+from mercurial import util
+
+class namespaces(object):
+    """
+    provides an interface to register a generic many-to-many mapping between
+    some (namespaced) names and nodes. The goal here is to control the
+    pollution of jamming things into tags or bookmarks (in extension-land) and
+    to simplify internal bits of mercurial: log output, tab completion, etc.
+
+    More precisely, we define a list of names (the namespace) and  a mapping of
+    names to nodes. This name mapping returns a list of nodes.
+
+    Furthermore, each name mapping will be passed a name to lookup which might
+    not be in its domain. In this case, each method should return an empty list
+    and not raise an error.
+
+    We'll have a dictionary '_names' where each key is a namespace and
+    its value is a dictionary of functions:
+      'namemap': function that takes a name and returns a list of nodes
+    """
+
+    _names_version = 0
+
+    def __init__(self):
+        self._names = util.sortdict()