code: def replaceChild(self, child, content):
          
          if child not in self.children:
              raise Exception('child not-found')
          index = self.children.index(child)
          self.remove(child)
          if not isinstance(content, (list, tuple)):
              content = (content,)
          for node in content:
              self.children.insert(index, node.detach())
              node.parent = self
              index += 1
docs: Replace I{child} with the specified I{content}.
          @param child: A child element.
          @type child: L{Element}
          @param content: An element or collection of elements.
          @type content: L{Element} or [L{Element},]