def METHOD_NAME(self, node):
    """
    Append (set) the document root.
    @param node: A root L{Element} or name used to build
        the document root element.
    @type node: (L{Element}|str|None)
    """
    if isinstance(node, str):
        self.__root = Element(node)
        return
    if isinstance(node, Element):
        self.__root = node
        return