typedef enum { ... } SilcAttributePNFormat;

    The defined phone number formats.

    typedef enum {
      SILC_ATTRIBUTE_NUMBER_ITU_E164        = 0,      /* ITU E.164 */
      SILC_ATTRIBUTE_NUMBER_ITU_E123        = 1,      /* ITU E.123 */
      SILC_ATTRIBUTE_NUMBER_ENUM            = 2,      /* ENUM, RFC 3761 */
    } SilcAttributePNFormat;