Magento 2.x Component & Registration.php File

• Component module defines module Registration

//For Component Module Registration 

ComponentRegistrar::register(ComponentRegistrar::MODULE, '<VendorName_ModuleName>', __DIR__);

• The Module component of registration.php looks as follows:

<?php

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'VendorName_ModuleName',
    __DIR__
);

• Component theme defines theme Registration

// For Component Theme Registration

ComponentRegistrar::register(ComponentRegistrar::THEME, '<area>/<vendor>/<theme name>', __DIR__);

• The Theme component of registration.php looks as follows:

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::THEME,
    'frontend/vendor/custom-theme',
    __DIR__
);

• Component Language defines Language Registration

// For Component Libraries Registration
ComponentRegistrar::register(ComponentRegistrar::LANGUAGE, '<VendorName>_<Language packageName>', __DIR__);

• The Language component of registration.php looks as follows:

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::LANGUAGE,
    'vendor_sp_sp',
    __DIR__
);

• Component library defines library Registration

// For Component Theme Registration 
ComponentRegistrar::register(ComponentRegistrar::THEME, '//', __DIR__);