title: Extending Drupal 8 Core Module
body: <p>I'm new to Drupal and I had for the need of the client, to extend the functionalities of the Aggregator module which is part of the core of Drupal.</p>
  
  <p>So as I've not found clear documentation on this subject, I have duplicated the module, changing its namespace to prevent any updates and done my stuff, adding new fields in DB, extend the Item entity, update Parser and Processor.</p>
  
  <p>It's working...<strong>but this is bad practice</strong>. So I was wondering if Drupal offers natively (as it is based on Symfony) any kind of proper ways of extending Module Core/User.</p>