The path to a local HTML file.
def get_html_file() -> str: ... def set_html_file(value: str) -> None: ...
html_file = property(get_html_file, set_html_file)
This property may contain the path to the local HTML file. If this property is not empty, the contents of the file with that name will be appended to the text in message_html.
Note that this means that if message_html is empty, html_file is what will be sent to the server.