def sort_severity(value):
    """
    Map a given UpdateSeverity string representation to a numerical severity value.

    This is used to sort severities from low to high.

    Args:
        value (str): The human readable UpdateSeverity string.
    Returns:
        int: A number representing the sorting order of the given UpdateSeverity string, or 99 if an
            unknown value is given.
    """
    value_map = {'unspecified': 1, 'low': 2, 'medium': 3, 'high': 4,
        'urgent': 5}
    return value_map.get(value, 99)
