def METHOD_NAME(self):
    if "RevealHelpPreprocessor.url_prefix" in self.config:
        warn(
            "Please update RevealHelpPreprocessor.url_prefix to "
            "SlidesExporter.reveal_url_prefix in config files.",
            stacklevel=2,
        )
        return self.config.RevealHelpPreprocessor.url_prefix
    return "https://unpkg.com/reveal.js@4.0.2"