anchor.diff:  
         name = mkOption {
           example = "eth0";
  -        type = types.string;
  +        type = types.uniq types.string;
           description = "Name of the interface.";
         };
   
         ipAddress = mkOption {
           default = null;
           example = "10.0.0.1";
  -        type = types.nullOr types.string;
  +        type = types.nullOr (types.uniq types.string);
           description = ''
             IP address of the interface.  Leave empty to configure the
             interface using DHCP.
  
positive.code:       subnetMask = mkOption {
          default = "";
          example = "255.255.255.0";
          type = types.string;
          description = ''
            Subnet mask of the interface, specified as a bitmask.
            This is deprecated; use <option>prefixLength</option>
  
negative.code:       macAddress = mkOption {
          default = null;
          example = "00:11:22:33:44:55";
          type = types.nullOr (types.uniq types.string);
          description = ''
            MAC address of the interface. Leave empty to use the default.
          '';
  