private function validate() {
        foreach ($this->entries as $entry) {
            // first call the entry's own validation method
            // which will throw an exception if there's anything wrong
            $entry->validate();
            // now make sure that all links are in place
            foreach ($entry->links as $linkedid => $rel) {
                // the linked to entry exists
                if (!array_key_exists($linkedid, $this->entries)) {
                    $a = (object)array('rel' => $rel->type, 'to' => $linkedid, 'from' => $entry->id);
                    throw new portfolio_format_leap2a_exception('leap2a_nonexistantlink', 'portfolio', '', $a);
                }
                // and contains a link back to us
                if (!array_key_exists($entry->id, $this->entries[$linkedid]->links)) {

                }
                // we could later check that the reltypes were properly inverse, but nevermind for now.
            }
        }
    }