$days is an optional array that can contain information you want to specify for each day, including a location to link that day to, a stylesheet class for that day, and any content you want to appear for that day of the calendar. For example, an array passed for the days parameter might look something like this:
<?php
$days = array(
2=>array('/weblog/archive/2004/Jan/02','linked-day'),
3=>array('/weblog/archive/2004/Jan/03','linked-day'),
8=>array('/weblog/archive/2004/Jan/08','linked-day'),
22=>array('/weblog/archive/2004/Jan/22','linked-day'),
);
?>