def add_file(self, file_grp, content=None, **kwargs):
        """
        Add an output file. Creates an :class:`OcrdFile` to pass around and adds that to the
        OcrdMets OUTPUT section.
        """
        log.debug(
            'outputfile file_grp=%s local_filename=%s content=%s',
            file_grp,
            kwargs.get('local_filename'),
            content is not None)
        if content is not None and 'local_filename' not in kwargs:
            raise Exception("'content' was set but no 'local_filename'")

        oldpwd = os.getcwd()
        try:
            os.chdir(self.directory)
            if 'local_filename' in kwargs:
                local_filename_dir = kwargs['local_filename'].rsplit('/', 1)[0]
                if not os.path.isdir(local_filename_dir):
                    os.makedirs(local_filename_dir)
                if 'url' not in kwargs:
                    kwargs['url'] = kwargs['local_filename']

            #  print(kwargs)
            ret = self.mets.add_file(file_grp, **kwargs)

            if content is not None:
                with open(kwargs['local_filename'], 'wb') as f:
                    if isinstance(content, str):
                        content = bytes(content, 'utf-8')
                    f.write(content)
        finally:
            os.chdir(oldpwd)

        return ret
Add an output file. Creates an :class:`OcrdFile` to pass around and adds that to the
        OcrdMets OUTPUT section.