Return a new :class:`~aeneas.textfile.TextFile` object,
        rooted at the given node ``root``.

        :param root: the root node
        :type  root: :class:`~aeneas.tree.Tree`
        :rtype: :class:`~aeneas.textfile.TextFile`

def get_subtree(self, root):
        """
        Return a new :class:`~aeneas.textfile.TextFile` object,
        rooted at the given node ``root``.

        :param root: the root node
        :type  root: :class:`~aeneas.tree.Tree`
        :rtype: :class:`~aeneas.textfile.TextFile`
        """
        if not isinstance(root, Tree):
            self.log_exc(u"root is not an instance of Tree", None, True, TypeError)
        new_text_file = TextFile()
        new_text_file.fragments_tree = root
        return new_text_file