Period requires PHP 7.1.3 but the latest stable version of PHP.
Period is available on Packagist and can be installed using Composer.
$ composer require league/period
You can also use
Period without using Composer by downloading the library and using any other PSR-4 compatible autoloader.
Starting with version 3.2.
Period comes bundle with its own autoloader you can call as shown below:
<?php require 'path/to/league/period/autoload.php'; var_dump(Period::createFromDay('TODAY'));
path/to/league/repo represents the path where the library was extracted.