How to add inline UI elements that aren't part of the document?

[kasrak]

I'd like to render some text below the document text, similar to how in Slab there are these placeholders for "Add a title..." and "Type / for full options":

What's the best way to implement that?

[kasrak]

I tried quill.editor.scroll.attachUI(myCustomElement), but that puts the custom UI at the top. I'd like for it to be below all the document contents.