composer.notes

PHP versions

  We chose the supported versions of PHP by looking at the oldest version we
  can use if we restrict ourselves to using the current release of one or
  other of the following packages on packagist.org:

    guzzlehttp/psr7
    zendframework/zend-diactoros

  As it happens, the oldest supported version for each is the same: PHP
  5.4.0.