def _prepare_app(self, app):
        """
        Normalize app data, preparing it for the detection phase.
        """

        # Ensure these keys' values are lists
        for key in ['url', 'html', 'script', 'implies']:
            try:
                value = app[key]
            except KeyError:
                app[key] = []
            else:
                if not isinstance(value, list):
                    app[key] = [value]

        # Ensure these keys exist
        for key in ['headers', 'meta']:
            try:
                value = app[key]
            except KeyError:
                app[key] = {}

        # Ensure the 'meta' key is a dict
        obj = app['meta']
        if not isinstance(obj, dict):
            app['meta'] = {'generator': obj}

        # Ensure keys are lowercase
        for key in ['headers', 'meta']:
            obj = app[key]
            app[key] = {k.lower(): v for k, v in obj.items()}

        # Prepare regular expression patterns
        for key in ['url', 'html', 'script']:
            app[key] = [self._prepare_pattern(pattern) for pattern in app[key]]

        for key in ['headers', 'meta']:
            obj = app[key]
            for name, pattern in obj.items():
                obj[name] = self._prepare_pattern(obj[name])
Normalize app data, preparing it for the detection phase.