public function slice($offset, $limit=null) {
		$this->rewind();
		$i=0;
		$del=array();
		while ($this->valid()) {
			if ($i < $offset)
				$del[]=$this->key();
			elseif ($i >= $offset && $limit && $i >= ($offset+$limit))
				$del[]=$this->key();
			$i++;
			$this->next();
		}
		foreach ($del as $ii)
			unset($this[$ii]);
	}