append(): Clarify the expected type of charset.
diff --git a/Lib/email/Header.py b/Lib/email/Header.py
index e02ccb8..9060fbb 100644
--- a/Lib/email/Header.py
+++ b/Lib/email/Header.py
@@ -151,7 +151,8 @@
def append(self, s, charset=None):
"""Append string s with Charset charset to the MIME header.
- charset defaults to the one given in the class constructor.
+ charset defaults to the one given in the class constructor. If
+ charset is given, it should be an instance of email.Charset.Charset.
"""
if charset is None:
charset = self._charset