Allow using flag for normalization.

README.md

@@ -718,18 +718,23 @@ $validator = new Validator($yourAdapter);
 
 [**Flag**](./src/Rule/Flag.php)
 
-- **Purpose**: Enforces that a value is either `true` or `false` (a boolean flag).
+- **Purpose**: Enforces that a value is either `true` or `false` (a boolean flag)
+  and [normalizes](#accessing-normalized-data) it if necessary.
 - **Options**:
-    - `value` (boolean): Specifies whether the rule requires the value to be `true` or `false`.
+    - `value` (boolean, default `null`): Enforces a specific value for the flag (true or false). Defaults to allowing
+      both `true` and `false`.
 - **Examples**:
   ```php
   use Norvica\Validation\Rule\Flag;
+
+  // normalized result will contain the boolean value (`true` or `false`)
+  $rule = new Flag();
 
   // ensure value is `false`
   $rule = new Flag(value: false);
 
   // ensure value is `true`
-  $rule = new Flag(value: false);
+  $rule = new Flag(value: true);
   ```
 
 [**Hostname**](./src/Rule/Hostname.php)

src/Rule/Flag.php

@@ -14,7 +14,7 @@
 readonly class Flag implements Rule, Normalizable
 {
     public function __construct(
-        public bool $value,
+        public bool|null $value = null,
     ) {
     }
 

src/Validation/FlagValidation.php

@@ -11,6 +11,11 @@ final class FlagValidation
 {
     public function __invoke(bool $value, Flag $rule): void
     {
+        // both `true` and `false` are allowed
+        if ($rule->value === null) {
+            return;
+        }
+
         if ($value !== $rule->value) {
             $parameter = $rule->value ? 'true' : 'false';
 

tests/Single/FlagTest.php

@@ -55,4 +55,10 @@ public function testOffInvalid(mixed $value): void
     {
         $this->assertInvalid($value, new Flag(false));
     }
+
+    public function testAnyBoolean(): void
+    {
+        $this->assertValid(true, new Flag());
+        $this->assertValid(false, new Flag());
+    }
 }