Webmozart\Console\Api\Args\Format\CommandOption::assertShortAliasValid PHP Method

    private function assertShortAliasValid($alias)
    {
        Assert::string($alias, 'An option alias must be a string or null. Got: %s');
        Assert::notEmpty($alias, 'An option alias must not be empty.');
        Assert::regex($alias, '~^[a-zA-Z]$~', 'A short option alias must be exactly one letter. Got: "%s"');
    }