public function getPreviousSibling()
	{
		$previous = null;
		
		// if this element has an index
		if (false !== ($index = $this->getIndex())) {
			// if this element has a previous sibling
			if ($this->parent->hasChild($index - 1)) {
				$previous = $this->parent->getChild($index - 1);
			}
		}
		
		return $previous;
	}