code: function findPrevRowNode(node){
  	var i, last, prev,
  		parent = node.parent,
  		siblings = parent ? parent.children : null;
  
  	if(siblings && siblings.length > 1 && siblings[0] !== node){
  		// use the lowest descendant of the preceeding sibling
  		i = $.inArray(node, siblings);
  		prev = siblings[i - 1];
  		_assert(prev.tr);
  		// descend to lowest child (with a <tr> tag)
  		while(prev.children){
  			last = prev.children[prev.children.length - 1];
  			if(!last.tr){
  				break;
  			}
  			prev = last;
  		}
  	}else{
  		// if there is no preceding sibling, use the direct parent
  		prev = parent;
  	}
  	return prev;
  }
docs: /* Find node that is rendered in previous row.