Symphony.

So I am trying to make necessary changes to make Dynamic Section Editor compatible with 2.3. I am currently stuck trying to get the html output and altering it of a backend page.

I tried the code below but output doesn't seem to be passed in the context array.

$context = Administration::instance()->Page->getContext();
$dom = DOMDocument::loadHTML($context['output']);

The backend is generated using XMLElement which is not flattened into the HTML markup until the very last second.

The various XMLElement's to generate a page are available as public variables of the AdministrationPage class, so you can access them like Administration::instance()->Page->Contents.

If this seems convoluted it's because it is a little, #1463 is the feature request to be able to modify the backend using XSL, so essentially the backend customisation is just like the frontend. We aren't at the point where that is doable yet, and probably won't be for a little while yet, but there are some experiments where extension developers have done so.