\subsection{Mailbox Objects \label{mailbox-objects}}
-All implementations of Mailbox objects are iterator objects, and so
-have one externally visible method:
+All implementations of mailbox objects are iterable objects, and
+have one externally visible method. This method is used by iterators
+created from mailbox objects and may also be used directly.
\begin{methoddesc}[mailbox]{next}{}
Return the next message in the mailbox, created with the optional