diff --git a/IPython/frontend/html/notebook/notebookmanager.py b/IPython/frontend/html/notebook/notebookmanager.py
index aaa9fbee0..18daf9ac0 100644
--- a/IPython/frontend/html/notebook/notebookmanager.py
+++ b/IPython/frontend/html/notebook/notebookmanager.py
@@ -237,7 +237,12 @@ class NotebookManager(LoggingConfigurable):
         self.delete_notebook_id(notebook_id)
 
     def increment_filename(self, basename):
-        """Return a non-used filename of the form basename0."""
+        """Return a non-used filename of the form basename<int>.
+        
+        This searches through the filenames (basename0, basename1, ...)
+        until is find one that is not already being used. It is used to
+        create Untitled and Copy names that are unique.
+        """
         i = 0
         while True:
             name = u'%s%i' % (basename,i)