PL/SQL Function: self-contained transaction?

In PostgreSQL, as everyone knows, a QUERY == a transaction, unless wrap'd 
in a BEGIN/END explicitly ... how does that work with a function?  is 
there an implicit BEGIN/END around the whole transaction, or each QUERY 
within the function itself?

If the whole function (and all QUERYs inside of it) are considered one 
transaction, can you do a begin/end within the function itself to 'force' 
commit on a specific part of the function?

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Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email: scrappy@hub.org           Yahoo!: yscrappy              ICQ: 7615664