def METHOD_NAME(self, markdown=None, markdown_file=None):
    """
    Updates the wiki's markdown. Specify only one of markdown or markdown_file
    :param markdown:        text that will become the markdown
    :param markdown_file:   path to a file. Its contents will be the markdown
    """
    if markdown and markdown_file:
        raise ValueError("Please use only one argument: markdown or markdownFile")
    if markdown_file:
        # pop the 'markdownFile' kwargs because we don't actually need it in the dictionary to upload to synapse
        markdown_path = os.path.expandvars(os.path.expanduser(markdown_file))
        if not os.path.isfile(markdown_path):
            raise ValueError(markdown_file + "is not a valid file")
        with open(markdown_path, "r") as opened_markdown_file:
            markdown = opened_markdown_file.read()
    self["markdown"] = markdown