(PHP 4 >= 4.2.0)
DomNode::replace_node — Replaces node
   (PHP 4.2) This function replaces an existing node with the passed
   new node. Before the replacement
   newnode is copied if it has a parent to
   make sure a node which is
   already in the document will not be inserted a second time. This
   behaviour enforces doing all modifications on the node before the
   replacement or to refetch the inserted node afterwards with functions like
   domnode_first_child(),
   domnode_child_nodes() etc..
  
   (PHP 4.3) This function replaces an existing node with the passed new node. It is not
   copied anymore. If newnode  was already inserted in the document 
   it is first unlinked from its existing context. If the replacement succeeds the old 
   node is returned. 
  
See also domnode_append_child()