[fw-gdata] Calendar - retrieving just some properties

Hi, I've got my gdata-php app retrieving my calendar,

And I'm looking at http://framework.zend.com/manual/en/zend.gdata.calendar.html

I see from the example that I can echo properties like:

foreach ($eventFeed as $event) {
echo "<li>" . $event->title . " (Event ID: " . $event->id . ")</li>";
}

And the document says I can use "Additional properties such as ID,
author, when, event status, visibility, web content, and content,
among others ..."

I don't want title, or summary, or id, I just want the event date, or
better yet, the date and busy/free.

But $event->when returns "array" and I don't know what its
sub-properties are or how to access them.

Thanks for any help