diff --git a/presubmit_support.py b/presubmit_support.py
index b7cf13afc3..cf15c9de40 100755
--- a/presubmit_support.py
+++ b/presubmit_support.py
@@ -766,8 +766,10 @@ class InputApi(object):
     If files_to_check or files_to_skip is None, InputApi.DEFAULT_FILES_TO_CHECK
     and InputApi.DEFAULT_FILES_TO_SKIP is used respectively.
 
-    The lists will be compiled as regular expression and
-    AffectedFile.LocalPath() needs to pass both list.
+    affected_file.LocalPath() needs to re.match an entry in the files_to_check
+    list and not re.match any entries in the files_to_skip list.
+    '/' path separators should be used in the regular expressions and will work
+    on Windows as well as other platforms.
 
     Note: Copy-paste this function to suit your needs or use a lambda function.
     """