[PATCH 4 of 7 🚂] transaction: document startgroup and endgroup

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1415181615 0
#      Wed Nov 05 10:00:15 2014 +0000
# Node ID 98d4dd03994f46807a06ec13ef5d1d1678366cb7
# Parent  eb05028743f69b00b2f5ab62d60880a6514875e2
transaction: document startgroup and endgroup

These enigmatic method are only used in repair. We document them to clarify
there purpose and user.

diff --git a/mercurial/transaction.py b/mercurial/transaction.py
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -115,14 +115,22 @@ class transaction(object):
         if self.journal:
             self._abort()
 
     @active
     def startgroup(self):
+        """delay registration of file entry
+
+        This is used by strip to delay vision of strip offset. The transaction
+        see either none or all strip action to be done."""
         self._queue.append(([], []))
 
     @active
     def endgroup(self):
+        """apply delayed registration of file entry.
+
+        This is used by strip to delay vision of strip offset. The transaction
+        see either none or all strip action to be done."""
         q = self._queue.pop()
         self.entries.extend(q[0])
         self._backupentries.extend(q[1])
 
         offsets = []