$validator = new Validator();

if ($validator->expectExactlyKeys($data, $keys) === true) {
    // ...
}

$data = [ // data
    'tags' => [],
    'name' => 'foobar'
];
$validation = new Validation($data);

$validation
    ->expectExactlyKeys(['tags', 'name'])
    ->expectKeyToBeArray('tags');
    ->expectKeyToBeString('name');

if ($validation->hasErrors()) {
    // $lastError = $validation->getLastError();
    // $errors = $validation->getErrors();
}

$validation = new StrictValidation($data);

// will throw an exception if any of tests below fail
$validation
    ->expectOnlyKeys(['id', 'title', 'description', 'isPrivate', 'tags'])
    ->expectAtLeastKeys(['id', 'title', 'description'])
    ->expectKeyToBeInteger('id')
    ->expectKeysToBeString(['title', 'description'])
    ->expectKeyToBeBoolean('isPrivate')
    ->expectKeyToBeArray('tags');

// if we reach this point, it means the array structure is
// valid according to the validation rules above.

$vDef = new ValidationDefinition();
$vDef
    ->expectOnlyKeys(['title', 'content', 'description'])
    ->expectAtLeastKeys(['title', 'content'])
    ->expectKeysToBeString(['title', 'content', 'description']);

$validation = new ValidationFromDefinition($vDef, $data);

if ($validation->hasErrors()) {
    // $validation->getErrors();
}

$mySchema = [
    'title' => [
        'type' => 'string',
        'required' => true
    ],
    'content' => [
        'type' => 'string',
        'nullable' => true,
    ],
];

$schema = new Schema(new SchemaCompiler(), $mySchema, 'mySchemaName');

$validation = new ValidationFromSchema($schema, $data);

if ($validation->hasErrors()) {
    // $validation->getErrors();
}

// all validation definitions are executed at object creation and an exception is thrown if any of tests failed
new StrictValidationFromDefinition($validationDefinition, $arrayToValidate);

// all validation definitions are executed at object creation and an exception is thrown if any of tests failed
new StrictValidationFromSchema($schema, $arrayToValidate);

$validation = new ValidationBuilder();
$validation
    ->expectOnlyKeys(['title', 'content', 'description'])
    ->expectAtLeastKeys(['title', 'content'])
    ->expectKeysToBeString(['title', 'content', 'description']);

if ($validation->validate($data) === false)  {
    // $validation->getErrors();
    // $validation->getLastError();
}

//  will throw an exception if any of tests fail
$validation->strictValidate($data);

interface ValidationInterface
{
    public function expectExactlyKeys(array $keys);
    public function expectOnlyOneFromKeys( array $keys);
    public function expectAtLeastKeys(array $keys);
    public function expectOnlyKeys(array $keys);
    public function expectNKeys(int $n);
    public function expectKeyToBeArray(string $key, bool $acceptNull = false);
    public function expectKeysToBeArray(array $keys, bool $acceptNull = false);
    public function expectKeyToBeInteger(string $key, bool $acceptNull = false);
    public function expectKeysToBeInteger(array $keys, bool $acceptNull = false);
    public function expectKeyToBeFloat(string $key, bool $acceptNull = false);
    public function expectKeysToBeFloat(array $keys, bool $acceptNull = false);
    public function expectKeyToBeString(string $key, bool $acceptNull = false);
    public function expectKeysToBeString(array $keys, bool $acceptNull = false);
    public function expectKeyToBeBoolean(string $key, bool $acceptNull = false);
    public function expectKeysToBeBoolean(array $keys, bool $acceptNull = false);
    public function expectKeyToBeObject(string $key, bool $acceptNull = false);
    public function expectKeysToBeObject(array $keys, bool $acceptNull = false);
}