diff --git a/mercurial/phases.py b/mercurial/phases.py
index 97528adbf74b30335b67cc21d88046d58fa564af_bWVyY3VyaWFsL3BoYXNlcy5weQ==..a13c18c14ade55515fdee74b9eedc39d047c4d6a_bWVyY3VyaWFsL3BoYXNlcy5weQ== 100644
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -171,6 +171,7 @@
         return ph
 
     def replace(self, phcache):
+        """replace all values in 'self' with content of phcache"""
         for a in 'phaseroots dirty opener _phaserevs _phasesets'.split():
             setattr(self, a, getattr(phcache, a))