Synchronous standbys?

Reading documents coming with Simon's patches, I'm a little bit
confused by the idea of "synchronous standbys".

In the sgmls doc, "The commit wait will last until the first reply
from any standby. Multiple standby servers allow increased
availability and possibly increase performance as well."

So in my understanding there could be one or more synchronous
standbys. However in his mail:

"If the current synchronous standby dies then one of the other
standbys will take over."

It seems there's only one synchronous standby allowed at the same
time.

Does anybody know which one is correct?
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp