ExampleRenderer.php

<?php

use ILIAS\UI\Implementation\Component\Button\Bulky;
use ILIAS\UI\Implementation\Render\DecoratedRenderer;
use ILIAS\UI\Renderer;

//inherit from DecoratedRender to align your renderer with other potential renders in ILIAS to allow manipulations from
//different sources to be chained behind each other.
class ExampleRenderer extends DecoratedRenderer
{
    //define your manipulations. This example add an "A" before every button in ILIAS
    protected function manipulateRendering($component, Renderer $root) : ?string
    {
        //select the component you want to manipulate
        if ($component instanceof Bulky) {
            //if you need the origin rendering (e.g. for append or prepend) you can access it by calling renderDefault()
            return "A" . $this->renderDefault($component, $root);
        }

        //skip components that are not important to you with returning null
        return null;
    }
}