1 files changed, 16 insertions, 9 deletions

diff --git a/src/mailman/interfaces/mailinglist.py b/src/mailman/interfaces/mailinglist.py
index 7f3b68008..0be8c2b68 100644
--- a/src/mailman/interfaces/mailinglist.py
+++ b/src/mailman/interfaces/mailinglist.py
@@ -20,6 +20,7 @@
 __all__ = [
     'IAcceptableAlias',
     'IAcceptableAliasSet',
+    'IHeaderMatch',
     'IListArchiver',
     'IListArchiverSet',
     'IMailingList',
@@ -843,7 +844,7 @@ class IListArchiverSet(Interface):
 
 
 class IHeaderMatch(Interface):
-    """A header matching rule for mailinglist messages."""
+    """A mailing list-specific message header matching rule."""
 
     mailing_list = Attribute(
         """The mailing list for the header match.""")
@@ -868,26 +869,32 @@ class IHeaderMatchSet(Interface):
     def clear():
         """Clear the set of header matching rules."""
 
-    def add(header, pattern, chain):
-        """Add the given header matching rule to this mailinglist's set.
+    def add(header, pattern, chain=None):
+        """Add the given header matching rule to this mailing list's set.
 
-        :param header: The email header to filter on. It will be converted to
-            lowercase for easier removal.
+        :param header: The email header to filter on.  It will be converted to
+            lower case for consistency.
         :type header: string
         :param pattern: The regular expression to use.
         :type pattern: string
         :param chain: The chain to jump to, or None to use the site-wide
-            configuration. Defaults to None.
+            configuration.  Defaults to None.
         :type chain: string or None
-        :raises ValueError: there can be only one couple of header and pattern
-            for a mailinglist.
+        :raises ValueError: if the header/pattern pair already exists for this
+            mailing list.
         """
 
     def remove(header, pattern):
-        """Remove the given header matching rule from this mailinglist's set.
+        """Remove the given header matching rule from this mailing list's set.
 
         :param header: The email header part of the rule to be removed.
         :type header: string
         :param pattern: The regular expression part of the rule to be removed.
         :type pattern: string
         """
+
+    def __iter__():
+        """An iterator over all the IHeaderMatches defined in this set.
+
+        :return: iterator over `IHeaderMatch`.
+        """