def severity_updateinfo_str(value):
    """
    Convert a severity level into one apt for inclusion in the updateinfo XML.

    These values are compatible with RHEL repodata to make it easier to write
    portable clients.

    Args:
        value (str): The Bodhi severity to be mapped to a repodata severity string.
    Returns:
        str: A severity string to be included in repodata.
    """
    severity_map = {'unspecified': 'None', 'low': 'Low', 'medium':
        'Moderate', 'high': 'Important', 'urgent': 'Critical'}
    return severity_map.get(value, 'None')
