Multiple Received-SPF headers

draft-schlitt-spf-classic-02 makes a reference to the possibility of having
multiple Received-SPF records.

What are the typical reasons why there might be multiple Received-SPF
headers?

If so,  how should it be handled?  Which one prevails, which one is show to
users, if done?

Only the last one added (top most header)?

Thanks

--
Hector Santos, Santronics Software, Inc.
http://www.santronics.com