def package_description(package):
    """Retrieves the STIX package description (str) from the header."""
    if package.reports and package.reports[0].header and package.reports[0].header.description:
        # STIX 1.2+
        return str(package.reports[0].header.description)
    elif package.stix_header and package.stix_header.description:
        return str(package.stix_header.description)
    else:
        return None