When are cond-expressions evaluated?

"c64zottel ." <[email protected]> Mon, 2 Jun 2014 11:46:39 +0200
Newsgroups gmane.comp.web.voice
Message-ID <CAL4YH=PWzNB9qmNAH5FZuuX8fyhE6GR3PMhVSY38-DLKmbEVxg@mail.gmail.com>
Hello,

if there is a statement like <state id="s" cond="a==7" />. When is the
cond-expression evaluate? Every time a changes and s is active?
Or just when an event occurs?

Regards.

Andreas