anchor.diff:      };
   
       fadeDelta = mkOption {
  -      type = types.int;
  +      type = types.addCheck types.int (x: x > 0);
         default = 10;
         example = 5;
         description = ''
  
positive.code:     };
  
      shadowOffsets = mkOption {
        type = types.listOf types.int;
        default = [ (-15) (-15) ];
        example = [ (-10) (-15) ];
        description = ''
  
negative.code: 
    cfg = config.services.compton;
  
    floatBetween = a: b: with lib; with types;
      addCheck str (x: versionAtLeast x a && versionOlder x b);
  
    pairOf = x: with types; addCheck (listOf x) (y: lib.length y == 2);
  
    opacityRules = optionalString (length cfg.opacityRules != 0)
      (concatMapStringsSep ",\n" (rule: ''"${rule}"'') cfg.opacityRules);
  
    configFile = pkgs.writeText "compton.conf"
      (optionalString cfg.fade ''
        # fading
        fading = true;
  