How to handle special use folders in Sieve?

[OBATA Akio]

Hi,

Since 3.0.0-beta2 release note's "Major changes since the 2.5.x series":

* Sieve now supports special use folders. See Cyrus Sieve

  http://cyrusimap.org/imap/admin/sieve.html#cyrus-sieve-specialuse

But I cannot find how to do it in sieve script.

For example, how to rewrite following script with such feature?

   if header :is "X-Spam-Flag" "YES" {
     fileinto "INBOX.Junk"
   }

-- 
OBATA Akio / obata at lins.jp