xenforo 2 development

Hello, we are planning to buy the XenForo 2 license. We will be having custom development and we need to hire resources that could maintain our site. With that, I would just like to inquire what PHP framework XenForo 2 is currently using?

I am getting below error while following "xf-addon:install-step" step from dev doc. An exception occurred: [TypeError] Argument 1 passed to Demo\Portal\Setup::Demo\Portal\{closure}() must be an instance of Demo\Portal\Alter, instance of XF\Db\Schema\Alter given, called in...