Constructor.
float $origin The origin time in milliseconds:
string $category The event category:
\InvalidArgumentException When the raw time is not valid
public function __construct($origin, $category = null) {
$this->origin = $this
->formatTime($origin);
$this->category = is_string($category) ? $category : 'default';
$this->started = array();
$this->periods = array();
}