javascript Node nextSibling, previousSibling

Return a reference to the next or previous node (respectively) in the document tree at the same nested level as the current node. If there is no node in the position indicated by the property name, the property returns null. For a lone text node inside an element node, both properties return null. Node sequence is determined intially by source code order, but script changes to the document tree are reflected in the nodes returned by these properties.