code: def set_node_text(self, node, text):
          
          # Remove any existing Text node children
          for child in self.get_node_children(node):
              if child.nodeType == xml.dom.Node.TEXT_NODE:
                  self.remove_node_child(node, child, True)
          if text is not None:
              text_node = self.new_impl_text(text)
              self.add_node_child(node, text_node)
docs: Set text value as sole Text child node of element; any existing
          Text nodes are removed