UniquePathAliasConstraint.php

<?php

namespace Drupal\Core\Path\Plugin\Validation\Constraint;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\Validation\Attribute\Constraint;
use Symfony\Component\Validator\Constraint as SymfonyConstraint;

/**
 * Validation constraint for unique path alias values.
 */
class UniquePathAliasConstraint extends SymfonyConstraint {
    
    /**
     * The default violation message.
     *
     * @var string
     */
    public $message = 'The alias %alias is already in use in this language.';
    
    /**
     * Violation message when the path alias exists with different capitalization.
     *
     * @var string
     */
    public $differentCapitalizationMessage = 'The alias %alias could not be added because it is already in use in this language with different capitalization: %stored_alias.';

}