Embed HedgeDoc content in HedgeDoc content

My version of HedgeDoc is: 1.9.8

What I expected to happen:

I understand that there are ways to embed external content on-the-fly. I also understand that some embedding is prohibited/or at least restricted unless you tweak the config.
What I would like to see happen is that content from one HedgeDoc file can become part of some other HedgeDoc file (to keep things simple: all on one installation) aka embedding by e.g. linking its address.

What actually happened:

Well if I iframe-it, that works; but that’s ugly with bouding box and all, giving you the feeling the content actually is from somewhere else.

I already tried:

Read the internet…