The recommended way to install EXT:extender is by using Composer:

composer require evoweb/extender

Add the extending classname to your packages Services.yaml and add a tag to it. The tag must contain the name 'extender.extends' and the class it is extending.

Services.yaml

services:

  Fixture\ExtendingExtension\Domain\Model\BlobExtend:
    tags:
      -
        name: 'extender.extends'
        class: Fixture\BaseExtension\Domain\Model\Blob