question: public Node replaceChild ( Node newChild , Node oldChild ) throws DOMException { if ( oldChild == null || oldChild . getParentNode ( ) != this ) return null ; ElemTemplateElement newChildElem = ( ( ElemTemplateElement ) newChild ) ; ElemTemplateElement oldChildElem = ( ( ElemTemplateElement ) oldChild ) ; ElemTemplateElement prev = ( ElemTemplateElement ) oldChildElem . getPreviousSibling ( ) ; if ( null != prev ) prev . m_nextSibling = newChildElem ; if ( m_firstChild == oldChildElem ) m_firstChild = newChildElem ; newChildElem . m_parentNode = this ; oldChildElem . m_parentNode = null ; newChildElem . m_nextSibling = oldChildElem . m_nextSibling ; oldChildElem . m_nextSibling = null ; return newChildElem ; }
target:  Replace the old child with a new child.