diff --git a/mercurial/repo.py b/mercurial/repo.py
--- a/mercurial/repo.py
+++ b/mercurial/repo.py
@@ -5,4 +5,19 @@
 # This software may be used and distributed according to the terms
 # of the GNU General Public License, incorporated herein by reference.
 
-class RepoError(Exception): pass
+class RepoError(Exception):
+    pass
+
+class repository(object):
+    def capable(self, name):
+        '''tell whether repo supports named capability.
+        return False if not supported.
+        if boolean capability, return True.
+        if string capability, return string.'''
+        name_eq = name + '='
+        for cap in self.capabilities:
+            if name == cap:
+                return True
+            if cap.startswith(name_eq):
+                return cap[len(name_eq):]
+        return False