diff --git a/src/CasesCollection.php b/src/CasesCollection.php
index c50fbea..60fff23 100644
--- a/src/CasesCollection.php
+++ b/src/CasesCollection.php
@@ -5,17 +5,18 @@
 use BackedEnum;
 use Countable;
 use IteratorAggregate;
+use JsonSerializable;
+use Stringable;
 use Traversable;
 
 /**
  * The collection of enum cases.
  *
- * @template TKey of array-key
  * @template TValue
  *
- * @implements IteratorAggregate<TKey, TValue>
+ * @implements IteratorAggregate<array-key, TValue>
  */
-class CasesCollection implements Countable, IteratorAggregate
+class CasesCollection implements Countable, IteratorAggregate, JsonSerializable, Stringable
 {
     /**
      * Whether the cases belong to a backed enum.
@@ -25,13 +26,31 @@ class CasesCollection implements Countable, IteratorAggregate
     /**
      * Instantiate the class.
      *
-     * @param array<TKey, TValue> $cases
+     * @param array<array-key, TValue> $cases
      */
-    final public function __construct(protected array $cases)
+    final public function __construct(protected readonly array $cases)
     {
         $this->enumIsBacked = reset($cases) instanceof BackedEnum;
     }
 
+    /**
+     * Turn the collection into a string.
+     */
+    public function __toString(): string
+    {
+        return (string) json_encode($this->jsonSerialize());
+    }
+
+    /**
+     * Turn the collection into a JSON serializable array.
+     *
+     * @return list<string|int>
+     */
+    public function jsonSerialize(): array
+    {
+        return $this->enumIsBacked ? $this->values() : $this->names();
+    }
+
     /**
      * Retrieve the count of cases.
      */
@@ -43,7 +62,7 @@ public function count(): int
     /**
      * Retrieve the iterable cases.
      *
-     * @return Traversable<TKey, TValue>
+     * @return Traversable<array-key, TValue>
      */
     public function getIterator(): Traversable
     {
@@ -53,24 +72,38 @@ public function getIterator(): Traversable
     /**
      * Retrieve all the cases as a plain array.
      *
-     * @return array<TKey, TValue>
+     * @return array<array-key, TValue>
      */
     public function all(): array
     {
         return $this->cases;
     }
 
+    /**
+     * Determine whether the collection contains the given case.
+     */
+    public function has(mixed $case): bool
+    {
+        foreach ($this->cases as $instance) {
+            if ($instance->is($case)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /**
      * Retrieve all the cases as a plain array recursively.
      *
-     * @return array<TKey, mixed>
+     * @return array<array-key, mixed>
      */
     public function toArray(): array
     {
         $array = [];
 
         foreach ($this->cases as $key => $value) {
-            $array[$key] = $value instanceof self ? $value->toArray() : $value;
+            $array[$key] = $value instanceof static ? $value->toArray() : $value;
         }
 
         return $array;
@@ -79,7 +112,7 @@ public function toArray(): array
     /**
      * Retrieve the first case.
      *
-     * @param (callable(TValue, TKey): bool)|null $callback
+     * @param (callable(TValue, array-key): bool)|null $callback
      * @return ?TValue
      */
     public function first(callable $callback = null): mixed
@@ -144,8 +177,8 @@ public function pluck(callable|string $value, callable|string $key = null): arra
      *
      * @template TMapValue
      *
-     * @param callable(TValue, TKey): TMapValue $callback
-     * @return array<TKey, TMapValue>
+     * @param callable(TValue, array-key): TMapValue $callback
+     * @return array<array-key, TMapValue>
      */
     public function map(callable $callback): array
     {
diff --git a/src/Concerns/Compares.php b/src/Concerns/Compares.php
index 4e4ba4c..5b8431c 100644
--- a/src/Concerns/Compares.php
+++ b/src/Concerns/Compares.php
@@ -26,13 +26,7 @@ public static function has(mixed $target): bool
      */
     public static function doesntHave(mixed $target): bool
     {
-        foreach (self::cases() as $case) {
-            if ($case->is($target)) {
-                return false;
-            }
-        }
-
-        return true;
+        return !self::has($target);
     }
 
     /**
@@ -74,12 +68,6 @@ public function in(iterable $targets): bool
      */
     public function notIn(iterable $targets): bool
     {
-        foreach ($targets as $target) {
-            if ($this->is($target)) {
-                return false;
-            }
-        }
-
-        return true;
+        return !$this->in($targets);
     }
 }
diff --git a/src/Concerns/SelfAware.php b/src/Concerns/SelfAware.php
index 4fa8834..db42c81 100644
--- a/src/Concerns/SelfAware.php
+++ b/src/Concerns/SelfAware.php
@@ -31,6 +31,22 @@ public static function isBacked(): bool
         return is_subclass_of(self::class, BackedEnum::class);
     }
 
+    /**
+     * Determine whether the enum is backed by integer.
+     */
+    public static function isBackedByInteger(): bool
+    {
+        return (new ReflectionEnum(self::class))->getBackingType()?->getName() === 'int';
+    }
+
+    /**
+     * Determine whether the enum is backed by string.
+     */
+    public static function isBackedByString(): bool
+    {
+        return (new ReflectionEnum(self::class))->getBackingType()?->getName() === 'string';
+    }
+
     /**
      * Retrieve all the meta names of the enum.
      *
@@ -41,12 +57,12 @@ public static function metaNames(): array
         $meta = [];
         $enum = new ReflectionEnum(self::class);
 
-        foreach ($enum->getAttributes(Meta::class) as $attribute) {
+        foreach ($enum->getAttributes(Meta::class, ReflectionAttribute::IS_INSTANCEOF) as $attribute) {
             array_push($meta, ...$attribute->newInstance()->names());
         }
 
         foreach ($enum->getCases() as $case) {
-            foreach ($case->getAttributes(Meta::class) as $attribute) {
+            foreach ($case->getAttributes(Meta::class, ReflectionAttribute::IS_INSTANCEOF) as $attribute) {
                 array_push($meta, ...$attribute->newInstance()->names());
             }
         }
diff --git a/src/Enums.php b/src/Enums.php
index 1ddc0aa..3c0d781 100644
--- a/src/Enums.php
+++ b/src/Enums.php
@@ -7,7 +7,7 @@
 use Closure;
 
 /**
- * The global behavior for all enums.
+ * The enums manager.
  */
 class Enums
 {
@@ -35,31 +35,31 @@ class Enums
     /**
      * Set the logic to run when an inaccessible enum method is called.
      *
-     * @param Closure(class-string $enum, string $name, array<array-key, mixed> $arguments): mixed $callback
+     * @param callable(class-string $enum, string $name, array<array-key, mixed> $arguments): mixed $callback
      */
-    public static function onStaticCall(Closure $callback): void
+    public static function onStaticCall(callable $callback): void
     {
-        static::$onStaticCall = $callback;
+        static::$onStaticCall = $callback(...);
     }
 
     /**
      * Set the logic to run when an inaccessible case method is called.
      *
-     * @param Closure(object $case, string $name, array<array-key, mixed> $arguments): mixed $callback
+     * @param callable(object $case, string $name, array<array-key, mixed> $arguments): mixed $callback
      */
-    public static function onCall(Closure $callback): void
+    public static function onCall(callable $callback): void
     {
-        static::$onCall = $callback;
+        static::$onCall = $callback(...);
     }
 
     /**
      * Set the logic to run when a case is invoked.
      *
-     * @param Closure(object $case, mixed ...$arguments): mixed $callback
+     * @param callable(object $case, mixed ...$arguments): mixed $callback
      */
-    public static function onInvoke(Closure $callback): void
+    public static function onInvoke(callable $callback): void
     {
-        static::$onInvoke = $callback;
+        static::$onInvoke = $callback(...);
     }
 
     /**
diff --git a/tests/BackedEnumTest.php b/tests/BackedEnumTest.php
index 74379ea..0d2545f 100644
--- a/tests/BackedEnumTest.php
+++ b/tests/BackedEnumTest.php
@@ -3,6 +3,7 @@
 use Cerbero\Enum\CasesCollection;
 use Cerbero\Enum\BackedEnum;
 use Cerbero\Enum\Enums;
+use Cerbero\Enum\PureEnum;
 use Pest\Expectation;
 
 it('determines whether the enum is pure')
@@ -13,6 +14,13 @@
     ->expect(BackedEnum::isBacked())
     ->toBeTrue();
 
+it('determines whether the enum is backed by integer or string', function() {
+    expect(BackedEnum::isBackedByInteger())->toBeTrue();
+    expect(BackedEnum::isBackedByString())->toBeFalse();
+    expect(PureEnum::isBackedByInteger())->toBeFalse();
+    expect(PureEnum::isBackedByString())->toBeFalse();
+});
+
 it('retrieves all the names of the cases')
     ->expect(BackedEnum::names())
     ->toBe(['one', 'two', 'three']);
diff --git a/tests/CasesCollectionTest.php b/tests/CasesCollectionTest.php
index 54e7bd7..7dcaeb6 100644
--- a/tests/CasesCollectionTest.php
+++ b/tests/CasesCollectionTest.php
@@ -5,11 +5,41 @@
 use Cerbero\Enum\PureEnum;
 use Pest\Expectation;
 
+it('turns into a JSON with pure cases', function() {
+    expect((string) new CasesCollection(PureEnum::cases()))
+        ->toBe('["one","two","three"]');
+});
+
+it('turns into a JSON with backed cases', function() {
+    expect((string) new CasesCollection(BackedEnum::cases()))
+        ->toBe('[1,2,3]');
+});
+
 it('retrieves all the cases')
     ->expect(new CasesCollection(PureEnum::cases()))
     ->all()
     ->toBe([PureEnum::one, PureEnum::two, PureEnum::three]);
 
+it('determines whether a pure collection contains an item', function() {
+    $collection = new CasesCollection(PureEnum::cases());
+
+    expect($collection->has(PureEnum::one))->toBeTrue();
+    expect($collection->has('one'))->toBeTrue();
+    expect($collection->has(BackedEnum::one))->toBeFalse();
+    expect($collection->has('four'))->toBeFalse();
+    expect($collection->has(1))->toBeFalse();
+});
+
+it('determines whether a backed collection contains an item', function() {
+    $collection = new CasesCollection(BackedEnum::cases());
+
+    expect($collection->has(BackedEnum::one))->toBeTrue();
+    expect($collection->has(1))->toBeTrue();
+    expect($collection->has(PureEnum::one))->toBeFalse();
+    expect($collection->has(4))->toBeFalse();
+    expect($collection->has('one'))->toBeFalse();
+});
+
 it('retrieves the count of all the cases')
     ->expect(new CasesCollection(PureEnum::cases()))
     ->count()