def getToplevelMessages(start=None, end=None, recent_first=True, sort_on=
    'date', filter_on='date', reversed=False):
    """Get a list of proxies for all messages that are at the top of a
           thread in order by date, optionally restricted to a specific date
           range and/or sorted by or filtered on the most recently responded 
           to message using the sort_on and filter_on arguments.

           The recent_first argument is deprecated and should no longer be used.
           It will be removed in a later version of the code."""
