diff --git a/mercurial/copies.py b/mercurial/copies.py
--- a/mercurial/copies.py
+++ b/mercurial/copies.py
@@ -370,8 +370,10 @@
         return {}, {}, {}, {}, {}
     elif copytracing == 'heuristics':
         return _heuristicscopytracing(repo, c1, c2, base)
+    elif copytracing in ['full', 'on']:
+        return _fullcopytracing(repo, c1, c2, base)
     else:
-        return _fullcopytracing(repo, c1, c2, base)
+        repo.ui.debug('unable to parse the copytracing mode %s' % copytracing)
 
 def _fullcopytracing(repo, c1, c2, base):
     """ The full copytracing algorithm which finds all the new files that were
@@ -379,7 +381,13 @@
     this file was copied from another file.
 
     This is pretty slow when a lot of changesets are involved but will track all
-    the copies.
+    the copies. Can be used by setting the following configuration:
+
+        [experimental]
+        copytrace = full
+
+    Also if you have set `experimental.copytrace=on`, this is the algorithm
+    which will be used.
     """
     # In certain scenarios (e.g. graft, update or rebase), base can be
     # overridden We still need to know a real common ancestor in this case We