/// <summary>
        /// Load state from an XML element
        /// </summary>
        /// <param name="xmlElement">XML element containing new state</param>
        public void LoadXml(System.Xml.XmlElement xmlElement)
        {
            XmlNamespaceManager xmlNamespaceManager;
            XmlNodeList         xmlNodeList;

            if (xmlElement == null)
            {
                throw new ArgumentNullException("xmlElement");
            }

            xmlNamespaceManager = new XmlNamespaceManager(xmlElement.OwnerDocument.NameTable);
            xmlNamespaceManager.AddNamespace("xsd", XadesSignedXml.XadesNamespaceUri);

            xmlNodeList = xmlElement.SelectNodes("xsd:SignaturePolicyId", xmlNamespaceManager);
            if (xmlNodeList.Count != 0)
            {
                this.signaturePolicyId = new SignaturePolicyId();
                this.signaturePolicyId.LoadXml((XmlElement)xmlNodeList.Item(0));
                this.signaturePolicyImplied = false;
            }
            else
            {
                xmlNodeList = xmlElement.SelectNodes("xsd:SignaturePolicyImplied", xmlNamespaceManager);
                if (xmlNodeList.Count != 0)
                {
                    this.signaturePolicyImplied = true;
                    this.signaturePolicyId      = null;
                }
                else
                {
                    throw new CryptographicException("SignaturePolicyId or SignaturePolicyImplied missing");
                }
            }
        }
 /// <summary>
 /// Default constructor
 /// </summary>
 public SignaturePolicyIdentifier()
 {
     this.signaturePolicyId      = new SignaturePolicyId();
     this.signaturePolicyImplied = false;
 }